Using Reflectix / Rattletrap Incorrectly? - I am rethinking my insulation approach...

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Nomad_Elvis

Guest
Thank you for the extensive write-up, I tried to follow your points and got stuck on the last one. Are you saying that most of the stuff is not good except yours but you can’t share what it is because of IP?

George.
George, I am not trying to imply that "most of the stuff is not good except yours."
There weren't any additional product recommendations in the posts I deleted, just some elaboration and additional technical justification that probably amounted to beating a dead horse. That's part of the "science project" Hein referred to.

FWIW, I am not a vendor, nor am I associated in any way with any vendor of any of the products I mentioned in my first post.

Any links I provided to online vendors were presented mainly as an easy way to describe those products, all of which can be bought elsewhere.
If you find the same material for less somewhere else, you should buy it there (that's what I would do).

The upfitter that I design RVs for does not sell upfit products; they only sell completed vehicles.

However, in the course of my work, I have expended a lot of time over the years to find the best, most cost-effective materials.

My second post compares two materials (Thinsulate & Low-E) recommended by another poster (who is also a vendor), to some of the alternatives.
Manufacturer specifications and my testing indicate they do not perform as well for thermal insulation as the ones mentioned in my first post, which pretty much covered all the bases.

It's always prudent to check the manufacturer's specifications for any material under consideration.
I provided links to the specs, links to where some of the less commonplace materials can be purchased, and general guidelines on how to use them.
Specific installation methods & practices can make or break any upfit.

If the primary concern is noise reduction, different materials would be used, either along with, or instead of, the thermal insulation materials mentioned in my first post.

I hope that what I posted is helpful to anyone considering adding thermal insulation when upfitting a van.

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Nomad_Elvis

Guest
I kept thinking that the reason I had originally spec'd the Dow Tuff-R/Thermax was more than just being a more uniform/consistent product than, say "Rmax R-Matte."

So I dug into my collection of white paper PDFs, and in one of them ("Understanding Mean Temperature Phenomenon for Polyisocyanurate Insulations"),
I found this chart:

Legend descriptions:
2 pcf ccPF = 2 lb./CubicFoot Closed-Cell Polyurethane Foam (professional grade spray or pour foam)
XPS = eXtruded PolyStyrene foam (e.g.: Owens Corning FOAMULAR or Dow STYROFOAM sheathing)
SPF = Spray Polyurethane Foam (e.g.: Froth Pak)
1/2 pcf ocSPF = 1/2 lb./CubicFoot Open-Cell Polyurethane Foam (e.g.: Great Stuff)

3M Thinsulate is not shown on this chart, but if it was, it would be in the same range as Cellulose and Fiberglass Batt,
according to specs available from 3M: https://sprinter-source.com/forum/attachment.php?attachmentid=87161&d=1498234695
Thinsulate has about half the R-value per inch as Thermax.

As it turns out, Dow Thermax (and presumably Tuff-R, though I need to confirm that), significantly outperforms other Polyiso foams at low temperatures.
Here's a pertinent excerpt from the white paper:

Understanding Mean Temperature Phenomenon for Polyisocyanurate Insulations said:
"Although this graph includes many types of insulations--including polyisocyanurate foam insulation (shortened to “Polyiso” in the legend)--the type of polyisocyanurate foam insulation in the BSL Thermal Metric Project is only roofing Polyiso insulation, which is significantly different from THERMAX™ Brand Insulation, patented, designed and manufactured for wall applications. In fact, polyisocyanurate foams have a wide range of property variations as a result of varying/different proprietary formulations used by each manufacturer and for different grades of foam.

In Figure 3, the same graph has been altered to include the R-Value of THERMAX Brand Insulation at three different mean temperatures to show just how much the lack of THERMAX insulation data represents. This further illustrates how polyisocyanurate insulations can differ from one another. Wall-polyisocyanurate foams are designed to meet the fire and vertical application performance requirements through use of different chemical formulation, which inherently separates the Polyiso foam for walls from those used in roofs even if offered by the same manufacturer. The labeled THERMAX Brand Insulation R-Values are all above the 6.5 R-Value mark, significantly higher than the other polyisocyanurate insulations shown."

useful refs.:
THERMAX Product Comparison Guide
Dow THERMAX Brand Insulation
Dow TUFF-R Insulation

Dow MONSTERGRIP Liner Adhesive

(spray polyurethane foam adhesive that cures to bond fiberglass liner panels to prepared spray foam insulation)

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Nomad_Elvis

Guest
A few addendums:

...Either one of these can be applied directly to the inside of the sheet metal but needs 1/4" air gap at the very minimum between it and additional insulation, and preferably at least 1/2" (more than 3/4" adds nothing, according to specs from Dow, and JohnsManville). The bulk insulation added on the inside of that air gap should also have a foil (both Tuff-R & AP Foil do) facing the air gap...
Here's a chart from Dow on that:



More info from the Thermax (basic version) product information sheet:


Two high-elasticity adhesive/sealants I omitted from my first post, that may be of interest:
DuraLink 50 Super Adhesion Sealant ("DuraLink 50's adhesion to difficult surfaces permits its use on anodized metal and coatings such as Kynar PVDF.")
MasterSeal NP 150: Low-modulus hybrid sealant ("Superior adhesion results in a long-lasting bond; Low modulus to accommodate for joint movement: 100% extension with little stress on bond line")
Both are useful for creating the isolation needed when upfitting for maximum thermal & acoustic performance.

And these can be used for removable (with difficulty) attachment for inner panels, providing thermal & acoustic isolation:
3M Dual Lock Reclosable Fasteners

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Eka

New member
Looking at them
  • Dow Tuff-R, R-6.5/in, only 190F :thumbdown:
  • Dow Thermax, 250F, R-6.5/in :thumbup:
  • Johns Manvill AP Foil, 250F, only R-6.0/in, Ok
  • Rmax R-Matte, 250F, only R-6.0/in, Ok
R-0.5 per inch isn't much difference. Other properties could easily make another one better in an different situation.

Best insulation I've seen without resorting to vacuum insulation panels (VIP) is a R-7.5 per inch spray in foam. It could also handle over 240F. I forget the maker as I found it over a decade ago. VIPs can be R-22 to R-50+ per inch, but don't puncture their exterior skin or they reduce to normal. Great for making ice boxes in confined spaces, but bloody expensive for any other use. Also they are fragile, and I wonder if they would survive much road vibrations. They get used on sailboats to make long lasting ice boxes.

If not for cost, 3M VHB tape 4959F White, 1/4 in x 36 yd 120 mil, would be near perfect tape for holding Dow Thermax to the inside of the exterior skin. It has a 400F temperature handling, and is 3mm thick for an ok air gap. A tape or caulk that provides 1/8" air gap and handles at least 240F would be better. To attach a sheet of Thermax to the inside of the outer skin which is slightly curved, every few inches slice into the back of the Thermax with a mat knife to make a slit for bending. You may need to make the slits a couple directions to follow gentle compound curves. Greater curves may require foam removal. On the opposite side from the slits run a strip of the VHB tape. Also run one around the perimeter of the panel. Now remove the backings from the VBH tape strips, and carefully install the panel. It now can only be removed with a scraper so be very careful of placement.

  1. outer sheet metal
  2. air gap, even 1 mm will work
  3. reflective layer facing outer sheet metal
  4. bulk insulation
  5. reflective layer facing interior wall board
  6. air gap, even 1 mm will work
  7. interior wall board

If you think multiple reflective layers are helpful, keep them to the outside or inside of the bulk insulation, and have all the ones on the outside face outside, and all the ones on the inside face inside. Also have the back side of the reflective layers be highly absorptive of IR light. That way IR reflected by an inner layer is absorbed by the next layer out. From there it can radiate, convect, or conduct in or out. Radiate is the only one that will be roughly half in and half out. Convection and conduction will mostly follow the thermal gradient. Dewar bottles take this reflective layering to an extreme and do it in a vacuum. That way they get rid of the conduction and convection. That is pretty much the only way that multiple reflective layers works well.

If you use a bulk insulation like thinsulate, wrap it in reflective craft paper. Then take a net and spray one side of it with a contact adhesive. Now place the craft paper wrapped Thinsulate on it. Lift it up, and make sure the netting is attached to the foil face. Not it can be fitted into it's place in the wall. The holes in the netting provide the air gap. I haven't tried this idea. I just thought of it.

2. Radiant Barrier Foil, glued to skin
:crazy: Why bother? It won't help unless the glue is 100% IR invisible. Once you glued the reflective foil to the skin it is in contact, and poorly reflects IR. If you want the radiant barrier facing in, then it is doubly bad. It will trap any radiant heat until it is absorbed by the insulation or air gap air. Great in the winter, sucks very bad in the summer.
 
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Nomad_Elvis

Guest
2. Radiant Barrier Foil, glued to skin ...
:crazy: Why bother? It won't help unless the glue is 100% IR invisible. Once you glued the reflective foil to the skin it is in contact, and poorly reflects IR. If you want the radiant barrier facing in, then it is doubly bad. It will trap any radiant heat until it is absorbed by the insulation or air gap air. Great in the winter, sucks very bad in the summer.
It's not :crazy:
It's physics, corroborated by manufacturer specs where applicable, and verified by practical real-world testing.

Rather than 'bench-racing' this, anyone who wants to actually verify it can do so fairly easily.
Just be sure to expose test chambers to actual sunlight instead of the heat lamps so often shown in demonstrations designed for marketing purposes,
and be sure to calibrate the temperature recording devices (e.g.: Elitech RC-4) to one another by running all of them in the same chamber as a baseline.

Why bother? It won't help unless the glue is 100% IR invisible.
Virtually the entire heat flow within a solid (including a glue layer) is via conduction.
There is practically no convective heat flow and zero radiant heat flow within a solid.

Radiant heat flows from the surfaces, proportional to surface temperature, and affected by surface treatment.

There are two aspects of this: reflectivity and emissivity. Bare aluminum foil has very high infrared reflectivity, and very low infrared emissivity, meaning that not only does it reflect heat, it also doesn't readily emit radiant heat either: less than 10% as much radiant energy as high emissivity surfaces (e.g.: paint, plastic), all else being equal.

The OEM exterior sheet metal skin is painted on both sides, meaning that both surfaces have fairly high emissivity, and radiate heat roughly equally inward and outward.
Adding foil on the inside surface makes it have low emissivity, which causes the inside to radiate heat at a lower rate than the outside, all else being equal.

The adhesive used to apply a radiant barrier has almost nothing to do with the thermal effectiveness of the system described in my first post.
Nor does whether or not the radiant barrier has an acoustic dampening layer under it.

The goal of an insulation system designed to reduce solar-induced heat gain on a sunny summer day is to increase heat flow to the outside air, and decrease heat flow toward the interior space. Increasing outward heat rejection (dissipation) by *any* means also reduces inward radiant heat flux, because it reduces the surface temperature. The index that rates this (Solar Reflective Index) is *approximately* 80-85 for OEM white paint (obviously OEM white paints vary).
The best performing coatings have an SRI of over 110, so they reject (dissipate) heat from solar energy ~ 30% better than OEM paint.
Combining a high SRI exterior coating with a low emissivity inside surface results in a very high performance combination for this application.

If you want the radiant barrier facing in, then it is doubly bad. It will trap any radiant heat until it is absorbed by the insulation or air gap air.
My first post explains exactly why a radiant barrier on the inside of a vehicle's exterior skin reduces the inward radiant heat flow, as long as there is an air gap, and assuming the exterior of the vehicle is painted. It forces a relatively larger percentage of the heat absorbed from sunlight to be rejected (dissipated) outwardly to the atmosphere.

Whether or not the space (of which there isn't much to work with in an RV sidewall) occupied by the 1/4" to 1/2" air gap would be better used for bulk thermal insulation depends partly on intended climate and partly on whether or not the exact exterior profile allows application of the highest R-Value insulation, and some other factors. The air gap itself adds more than R2 (resistance to conductive heat flow), about the same as having typical thermal insulation in that same space.

Blocking external radiant energy with a foil-faced air gap only works *once* though; multiple foil-faced air gaps do not produce a similar result. While it is true that using only one foil radiant barrier adjacent to an air gap will provide more than half the benefit of a foil layer on both sides of an air gap, in this application (metal skin vehicle) that layer needs to be applied to the interior surface of the exterior metal skin. Given that the highest performing foam sheathings all have foil facers, it seems like a no-brainer to allow that to serve as the second radiant barrier on the inner side of the air gap.

If the RV is expected to be parked outside in daytime in warm, sunny areas, then adding the foil-airgap-foil works better overall than adding thermal insulation. Part of this is due to what should be obvious: sunlight is an intense source of radiant energy. A radiant barrier system that completely blocks that radiant energy makes practically the same difference as between parking out in the open (if the vehicle is parked there all day), or parking under a carport. But no internal radiant barrier system can match that; a similarly designed external shade system is required for that, which has practical limitations. The goal is to get as close as possible, while remaining as practical and cost-effective as possible.

It may be worth noting what is probably obvious to any RVer: cooling a parked RV is not as "easy" as heating it, which merely requires burning a very small amount of the same fuel the vehicle runs on. The electrical energy required to run air conditioning available from PV panels or stored in batteries is tiny in comparison. So that's one of the main reasons it's beneficial to optimize an RV insulation system to minimize heat gain from the exterior.

Best insulation I've seen without resorting to vacuum insulation panels (VIP) is a R-7.5 per inch spray in foam.
You may be able to buy spray-in foams that claim to have an R-value of 7.5 per inch, but no sprayed foam currently commercially available achieves anything like R7.5 per inch as installed, especially not the variants readily available to consumers, and especially not in an overhead installation where highest R-value is needed most. The reasons are fairly technical, but "consistency" is the main difference between a field-sprayed foam, and foam manufactured under controlled conditions in a factory.

Setting aside esoteric materials like aerogel or vacuum panels that nobody is ever going to use to insulate an RV, AFAIK there is only one commercially available foam that outperforms Thermax: Kingspan Kooltherm K8 phenolic foam (R-8.0 per inch). Check the price and you'll find out why I don't consider that - or other stuff like that - to be commonly available materials... even mentioning them moves this away from practicality and toward academic curiosity.

The current generally accepted "real-world" long-term R-Value for professionally sprayed closed-cell polyurethane foam is R-5.6 per inch, at 75°F.
Although it's not uncommon to find exaggerated claims, here's a pretty straightforward explanation, by a spray-foam installation company that uses the latest equipment (and is being honest). Their as-installed estimate is: R-5.1 to R-5.678 per inch.

My first post explains the reasons why, and the chart in this post above confirms it. If considering other Polyiso foams to be "only 0.5 R value per inch less than Dow Thermax or Tuff-R" and if cold weather performance is important, it would probably be worth determining if they perform more like the "Polyiso" curve on that chart, because as that chart shows, some polyiso foams have an R-Value curve that drops off a cliff in cold weather (google: "Polyiso Thermal Drift"). Considering the relatively small quantity of material needed, IMO it's worth specifying the best commonly available material, and let accounting analysts choose to cut corners.

If you think multiple reflective layers are helpful, keep them to the outside or inside of the bulk insulation, and have all the ones on the outside face outside, and all the ones on the inside face inside.
If you're referring to a radiant barrier on the inside of of the envelope (i.e.: used as an interior finish), that will reflect radiant energy from interior heat sources, but most of those (e.g.: body heat) are low intensity heat sources. That would also exacerbate control of exterior noise coming in through the windows while driving, and most people would consider it to be aesthetically unacceptable. :smirk:

.....

I hope that what I posted is self-explanatory enough to anyone who takes the time to read it,
and helpful to anyone considering adding thermal insulation when upfitting a van,
especially if it helps avoid the purchase/installation of over-priced, over-hyped materials.

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driveon

New member
Thank you very much to Nomad Elvis for providing a detailed and comprehensive analysis into a subject which is a treasure chest of online misinformation(i.e. Youtube DIY Van radiant barrier van install videos).

I have to respectfully disagree with Hein who stated this subject should not become a science project as that is one of the fundamental reasons why so much misinformation exist.

The lack of detailed scientific and longer term testing compared to half assed Youtube information and vendor marketing hype have all done the DIY van build community a major disservice.

I regret that Nomad Elvis was forced to delete some of his other posts as I encourage him or her to repost them for the benefit of the Sprinter Forum community .

Let all try to stay cool out there by using the educational resources and knowledge Nomad Elvis has provided for our benefit and comfort.

Sincerely,


Driveon
 

GeorgeRa

2013 Sprinter DIY 144WB, Portland OR
Thank you very much to Nomad Elvis for providing a detailed and comprehensive analysis into a subject which is a treasure chest of online misinformation(i.e. Youtube DIY Van radiant barrier van install videos).

I have to respectfully disagree with Hein who stated this subject should not become a science project as that is one of the fundamental reasons why so much misinformation exist.

The lack of detailed scientific and longer term testing compared to half assed Youtube information and vendor marketing hype have all done the DIY van build community a major disservice.

I regret that Nomad Elvis was forced to delete some of his other posts as I encourage him or her to repost them for the benefit of the Sprinter Forum community .

Let all try to stay cool out there by using the educational resources and knowledge Nomad Elvis has provided for our benefit and comfort.

Sincerely,


Driveon
I appreciate the data posted about insulation. I used Thinsulate on my van back in 2013, knew the product from the boating industry, friendly for installation, friendly for reworking, friendly for chassis repair in case of accident, good enough for sound, good enough for insulation, friendly for healthy air to breath – no VOC, good for low water vapor absorption and associated corrosion and low level of unintended issues in the marine industry, so, I used it and never look back. I run into the roof beams a few years back and the body shop was happy with easy access to pull out a slight dent.

Converting a van is a big project for a single person, multiple fields of knowledge are required so solar panels don’t turn into highway Frisbees, batteries don’t explode, wiring doesn’t fry, flying cabinets don’t kill you during a head-on accident, black water tank doesn’t jackknife under the van spilling the content, and all functionalities perform without hiccups.

So, there is a progress inhibiting level of analysis paralysis preventing multiple decisions to be made. Analytical folks, like myself, need to constantly fight falling into debilitating analysis paralysis down spirals.

Again, I appreciate the data, for a decision an information is needed and it takes time to digest all of the publish data and turn it to useful information leading to a selected choice. I am no longer in the process of selecting insulation so my head was not absorbing this data with ease, didn't have to.

George.
 
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Pvclemm

New member
for a given insulation level a white van will heat up significantly less than a dark or even mid range color. to get some objective view of the impact of color see a typical metal roof color chart which shows white has a solar reflectance of close to 3x a dark color. https://www.custombiltmetals.com/wp-content/uploads/2015/08/Standing_Seam_Roofing_Color_Chart.pdf


Also note that bare metal has a very poor "emittance" value meaning that it naturally will heat up regardless of how "mirror like" it looks (in post above aluminum tape is considered to cover the roof of the van. Much better to paint the roof white. Note also that the windshield and any other glass (none of which is insulated) has a large impact on heating the van regardless of how well insulated the van is.


Sent from my iPhone using Tapatalk
 

Gpaw68

2015 144 4cyl high roof
Looks like a combination of Thermax and thinsulate may be the way to go. I think 1/2 inch Thermax and a thinsulate layer might fit in the walls. Would give a good combination of both r value and acoustic dampening. What are the thoughts on this?
 
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Nomad_Elvis

Guest
for a given insulation level a white van will heat up significantly less than a dark or even mid range color. to get some objective view of the impact of color see a typical metal roof color chart which shows white has a solar reflectance of close to 3x a dark color. https://www.custombiltmetals.com/wp-content/uploads/2015/08/Standing_Seam_Roofing_Color_Chart.pdf
The highest SRI on that chart is Regal White, SRI: 87, which is about the same as OEM GM/Ford/Mercedes van white paint.

Also, "Custom Bilt Metals" manufactures metal roofing, and the chart is for pre-finished metal roof panels, not field-applied coatings.

For anyone who wants to repaint their RV exterior (or just the roof) with a coating that reflects the most heat from sunlight, here are a three examples of commonly available materials:

*Gardner Eterna-Kote S-100 Silicone coating (Home Depot), Initial SRI: 114-115
*BLACK JACK Premium Silicone Reflective Roof Coating (Lowes), Initial SRI: 114-115
Gardner Sta-Kool 805 Metal-X Acrylic coating (Home Depot), Initial SRI: 110

*same product, sold by the same company (Gardner) under different brand names.

For anyone who wants the very highest SRI coating available, AFAIK, this is it:
AcryShield Ultra-High Reflectance A590 (Not easy to buy in DIY quantities), Initial SRI: 117

You can look up the SRI and more info of almost all "cool roof" coatings here: CRRC Rated Products Directory

If it's not in that index, it's either just come on the market, or a possibly bogus product that doesn't even have a CRRC rating.


Also note that bare metal has a very poor "emittance" value meaning that it naturally will heat up regardless of how "mirror like" it looks...
Emittance pertains specifically to the rate of radiant heat emission.

How much a substance heats up when exposed to sunlight depends on how well it rejects (dissipates) heat by conduction, convection and radiation. Other factors affect this aside from emissivity.

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Nomad_Elvis

Guest
Looks like a combination of Thermax and thinsulate may be the way to go. I think 1/2 inch Thermax and a thinsulate layer might fit in the walls. Would give a good combination of both r value and acoustic dampening. What are the thoughts on this?
I must confess I had not taken a look at the interior structure that you have to work with on a late-model Sprinter until yesterday. I found this forum as a result of an unrelated search. All my work is with US vehicle platforms. Although the suggestions made in my previous posts are technically accurate and will be highly effective, applying them to some areas of late-model Sprinters might not be so easy.

It would not be easy to insert rigid foam into these lower wall cavities:


I'm not sure if the six round holes in the top of that horizontal mid-wall structural member provide passageways to the larger 'main' cavity below the horizontal member, but if they do (or can be added), that opens up another much easier possibility, especially if an OEM or aftermarket/DIY interior liner panel is added, as shown in this photo:



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Graphite Dave

Dave Orton
Elvis:

What is missing from your insulation chart is flexible closed cell foam. In Sprinter build I used small pieces of polyiso through he deep openings above and below the window indents and held in place with Great Stuff spray foam. Very tedious process.

Was at a brewery and noticed a contractor using Aerocel closed cell foam to insulate the beer tanks and piping. Bought that to insulate the deep openings in the Transit build. Easy to cut larger pieces and bend it to fit it through the openings then used Aeroseal contact adhesive. Bought 1" thick foam and used two layers against the van steel. Covered that with Reflectix and had about a 2" air gap to the 1/4" plywood wall covering. Aerocel has "R" value of 4.1/inch

http://www.aeroflexusa.com/wp-content/uploads/2016/11/Aerocel_EPDM-Black.pdf

Also suspect the foam has good noise reduction qualities.

Where would this method fit in your chart?

More detailed description of Transit insulation:

http://www.ortontransit.info/walls.php
 
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Nomad_Elvis

Guest
Admittedly, given the cavities in the lower section of the Sprinter's side walls, flexible material would have to be a lot easier to put in place inside those cavities than rigid foam. Thermax is most easily applied across the interior surface of ribs/stingers, as in the top section of the Sprinter side walls.

For those not concerned with meeting FMVSS 302, and looking for insulation that is...
1. very cheap,
2. very easy to install (no cutting or fitting),
3. causes no problem with sheet metal distortion,
...the easiest way is to pour in loose fill materials, such as tiny EPS beads, originally designed as a better alternative to vermiculite to fill hollow cavities like concrete blocks.

It can be poured in via gravity fill (large bag with a funnel outlet) and removed if need be using a shop-vac.

The tradeoff is, the tiny EPS bead fill yields an R-Value of only about R-2.5 per inch.
There is also a better performing version of EPS beads that recently came on the market: BASF Neopor.
Neopor supposedly has 20% better R-value for only 5% cost increase, but I suspect DIYers will have difficulty buying it.

You can use a similar approach with loose-fill fiberglass insulation in plastic bags (but eventual settling will necessitate topping off after the initial fill), and get slightly over R-4 per inch (@ 1.8 lb./CF fill).

This can also be done with 2-part flexible expanding foam (inside plastic bags if removability is desired), and get closer to R-6 per inch, but at a much higher cost. This also works with 2-part expanding foam (which is much less expensive, approaching the same cost as manufactured boards), but additional precautions must be taken to avoid sheet metal distortion due to expansion pressure.

All the above are "easy" - conforming well to irregular cavities, greatly minimizing waste, and eliminating most of the cutting & fitting required with any sheet material.

And here is another option, somewhat of a variation of the above, but it is manufactured in it's own plastic wrapper: Johns Manville ComfortTherm,
sold at most Lowes stores (R-13, 40 SF for $16.41).
JohnsManville said:
"JM ComfortTherm poly-encapsulated thermal and acoustical fiberglass insulation is lightweight and made of long resilient glass fibers. ComfortTherm is wrapped in plastic for more comfortable installation with less itch and dust. The product is available with a vapor-retarder plastic facing..."
It's about R-3 per inch. The cut ends should be closed off (taped) to avoid migration of the fibers.

...Aerocel closed cell foam... Bought that to insulate the deep openings in the Transit build. Easy to cut larger pieces and bend it to fit it through the openings then used Aeroseal contact adhesive. Bought 1" thick foam and used two layers against the van steel. Covered that with Reflectix and had about a 2" air gap to the 1/4" plywood wall covering. Aerocel has "R" value of 4.1/inch

http://www.aeroflexusa.com/wp-content/uploads/2016/11/Aerocel_EPDM-Black.pdf
Also suspect the foam has good noise reduction qualities.
Aerocel looks a lot like Armaflex.
There are a lot of similar closed cell foamed rubber products designed for piping and duct insulation.
They are typically more expensive than some of the alternatives, but I have not priced Aerocel.

They usually have good vibration dampening / acoustic attenuation characteristics, but not necessarily in the frequency range most problematical in a vehicle.
Still, from the NRC chart on the PDF you referenced, 1" thick Aerocel is not bad in this respect.

At R-4.1 per inch, 158% as much is needed to match the same R-value as TuffR/Thermax.
There is only so much space to work with in an RV sidewall, and that gives up a lot.

But the bottom line is only established when the cost is considered, so since you bought it, how much did it cost, for what thickness/size roll?

Update - here's the answer:
Graphite Dave via PM said:
Comes in 3' x 4' sheets
1" thick was $2.26/sq. ft. or $27.19/sheet
1/2" thick was $1.26/sq. ft. or $15.12/sheet
(Dave also posted this info below)

Density is omitted from the manufacturer's Aerocel TDS.
A quick search of their site did not yield any answer either.
Since you bought it, do you have a weight per roll (for what thickness/size roll?)

Elvis: What is missing from your insulation chart is flexible closed cell foam.
It's not my chart. It's the result of several series of tests, as mentioned on the chart:
"Published data adapted from BSL Thermal metric Project & Other recent Research by BSL & RDH – data may not be representative of all insulation types."

refs.: BSC Thermal Metric Project
Understanding Mean Temperature Phenomenon for Polyisocyanurate Insulations

BSC and Dow choose not to test flexible urethane foam. But the testing they did do was more than adequate for their purposes (and mine).

The factors that affect R-value of a closed-cell foam are pore size (how "coarse" or "fine" the foam is), closed cell percentage (what percentage of the cells are actually fully closed), permeability of the membrane between the cells, the exact nature of the gas contained within the cells. How well the gas remains entrapped in the cells is part of what determines long-term R-value.

It's worth noting that *no foam is 100% closed cell.*
Foams manufactured in carefully controlled conditions come closest.
One-component spray foams like "Great Stuff" fall farthest away from that goal; it typically performs more like open-cell foam, and it isn't that cheap ($/CF) either.

It is worth noting something I mentioned in my first post: flexible foam is required in some cases to prevent distortion if allowed to contact the exterior skin.
But it does not have to be used everywhere, which is a good thing, because it costs more than rigid foam.

And if only a radiant barrier is applied to the inner surface of the exterior sheet metal, there is no distortion. That scheme also compensates for irregularities (styling grooves, etc.) in the exterior skin.

Whether rigid vs. flexible, all closed-cell polyurethane foams created from similar chemical reactions have about the same R-value per inch, assuming a similarly well-controlled/fully-completed foaming process, and the *initial* theoretical R-value of most is claimed to be R-7.x per inch.

Here are examples of rigid and flexible polyurethane foams, both of which are claimed to be R-7.x per inch (initially):
3 LB/CF Flexible Urethane: 7.33 CubicFeet* for $134 = $18.28 per CF
2 LB/CF Rigid Urethane Foam: 8 CubicFeet* for $67 = $8.38 per CF

...and for reference:
DOW FROTH-PAK FOAM INSULATION 650 CLASS A, 54.2 CubicFeet* for $736.45 (typical price, here) = $13.59 per CF
Dow FROTH-PAK 650 Foam Insulation Kit, 54.2 CubicFeet* for $747.14 (Lowes) = $13.78 per CF
Dow FROTH-PAK 200 Foam Insulation Kit, 16.7 CubicFeet* for $359.68 (Lowes) = $21.54 per CF
VERSI-FOAM System 50, 50CubicFeet* for $664.35 (here) = $13.29 per CF

...lastly, sheet materials that have *tested* long-term R-value of 6.5 per inch:
Super Tuff-R, 1" thick x 4' x 8' , 2.66 CubicFeet for $15.95 (at Home Depots that stock it; not all do) = $6 per CF (but only at Home Depots that stock it).
TherMax, 1" thick x 4' x 8' , 2.66 CubicFeet for $33.29 (typical price, here) = $12.51 per CF

* typical maximum volume yield at rated density, under optimal conditions.

Of course, with any scheme, waste has to be taken into account.
For some applications, sheet materials have the lowest waste.
For others, the poured foams can have the lowest waste, if the amounts required are carefully calculated prior to mixing.

The bottom line is cost vs. performance vs. ease of installation.

I'd suggest using the costs provided above to calculate the cost for any given R-value, and taking into account that a $700+ kit is a steep price for a feet-wet exercise, considering that it takes a fair amount of skill to apply, and that the best case scenario still ends up with a higher cost per cubic foot per R-value than some other alternatives.

That way it's easy for anyone can draw their own conclusions and make their own tradeoffs as to what works best for their situation and budget.

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One last thing: most of the stuff sold by hytechsales.com is closer to bogus than reality (sort of like a multivitamin including just enough of something so they can claim they have it, but not enough to provide any real benefit). That's why their products don't have real, verifiable test results, and are not listed by industry rating agencies like the CRRC.
 
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bcman

Active member
Elvis, thanks for sharing your experience and knowledge. Here's one question I have about your preferred setup of foil+air gap+foil: what about convection of the air in the air gap? I would think that the 1/2-3/4" volume could transfer heat via convection pretty easily from one foil surface to the next, even if those air volumes are sealed. Ed touches on this in the video ("Solarguard will never achieve an R11 value in an attic with air flowing on both sides of the product.") Wouldn't a fiberglass/Thinsulate/low-density foam in this space reduce the convection, while still allowing the foil layers to do their job as a radiant barrier?

On my van, I was primarily concerned with noise, so I started out with a 3-pronged approach: CLD for the outer skin to damp vibration, Thinsulate SM600L to absorb high frequencies, and MLV hung behind the trim panels as a sound barrier. However, after installing the CLD (~50% coverage) and Thinsulate, I've been happy enough with the result that I've never gotten around to installing the MLV. To improve thermal insulation, I've been thinking I could hang Reflectix (or any other foil - I have Reflectix left over from window covers) behind the trim panels. Then I've got:

van skin > foil (CLD@50% coverage) > insulated air gap (Thinsulate) > foil (Reflectix) > trim panel

What do you think? Will I see a noticeable improvement in thermal performance by adding this layer of Reflectix?
 
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Nomad_Elvis

Guest
Here's a chart of Aerocel EPDM foam sheet compared to a few other selected 1" acoustic reduction foams:
(and I did create this chart):



As I sort of suspected, Aerocel EPDM foam sheet is very good at the lower end of the frequency range, but much lower than the other absorbers shown on this chart up in the audible range. Materials like this are often used as vibration dampeners for equipment. The difference in this case between a vibration dampener and an acoustic dampener is mainly whether or not it's audible, with "vibrations" being felt, rather than heard. Aerocel EPDM foam is probably an excellent choice for a few applications in a vehicle (similar to the high elasticity sealants I mentioned earlier), but probably not for overall application to thin sidewall sheet metal.

The primary noise range that needs to be controlled in most larger vans or heavy-duty pickup trucks is 250Hz-1000 Hz.

You can find out the frequency range for any vehicle quite easily by simply recording the sounds at various locations (for isolation, the closer to the source, the better), and then analyzing the frequency spectrum of those recordings on commonly available software.
 
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Nomad_Elvis

Guest
Elvis, thanks for sharing your experience and knowledge. Here's one question I have about your preferred setup of foil+air gap+foil: what about convection of the air in the air gap? I would think that the 1/2-3/4" volume could transfer heat via convection pretty easily from one foil surface to the next, even if those air volumes are sealed
That's why the perimeter must be closed off, because it minimizes (almost eliminates) convective flow.

Corroboration of the fact that having an air gap works is provided by the chart from Dow (above) which states that: "a non-ventilated 3/4" air space (R-value = 2.8)"
And, that is a typical value under test conditions where the chamber is indoors, not exposed to an intense infrared source (sunlight).

That's taken from this TDS, page 2, which cites the original source as the ASHRAE Fundamentals Handbook, which is used to determine HVAC loads.
These are the type of long-established, credible data sources used by professional engineers, not marketing-driven or fly-by-night hyperbole.

Since the main difference between glass and steel (in this context) is how much of the visible sunlight is converted to heat when it strikes the surface, it might be helpful to consider that the foil-airgap-foil arrangement described in my first post works on exactly the same principle as dual-pane Low-E windows, which are now so widely produced and sold by so many reputable manufacturers that common sense suggests it's not likely all of them have this wrong.

In fact, almost all Low-E windows have very similar metallic coatings (differing only in how they are specially formulated to allow more visible light to pass through) that are typically deposited onto the glass in the same way (vapor deposited) as the 'metalized' type of radiant barrier foil. The same is true of most metalized (not "tinted") solar-blocking window films. Both Low-E windows and solar reflective window film are available in different versions that let less light through (i.e.: the darker shades), and they are more like radiant barrier foil than their lighter counterparts. And the very cheapest radiant barrier materials actually let a very small amount of light through (barely visible if held up to the mid-day sun). Low-E glass and radiant barrier foil are really just variations of the same scheme.

If the air gap cavity has openings at top and bottom, convection will be mostly unimpeded: cooler air will be drawn into the bottom, and heated air will exit the top. It will work about the same whether it's a broken dual pane window or a poorly built RV sidewall. The result is an inadvertent solar thermal collector. Different variations of this, intentionally designed to provide solar heated air, are known as: "Trombe Walls."

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Nomad_Elvis

Guest
...To improve thermal insulation, I've been thinking I could hang Reflectix (or any other foil - I have Reflectix left over from window covers) behind the trim panels. Then I've got:

van skin > foil (CLD@50% coverage) > insulated air gap (Thinsulate) > foil (Reflectix) > trim panel

What do you think? Will I see a noticeable improvement in thermal performance by adding this layer of Reflectix?
Installing Reflectix under interior trim panels will add at most about R-1 to the total R-value of your conductive insulation. As a radiant barrier, it will reduce solar radiant heat gain by approximately zero, and reduce interior heat loss by so little that you probably couldn't measure it, partly because the inside of your van has no intense radiant heat sources, and partly because the under-the-interior-trim-panel location has little or no air gap (or so I assume).

If your existing window covers fit inside your windows, the best use for leftover Reflectix to reduce solar heat gain is probably external window covers, held in place by magnets and/or suction cups.

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moosevan

New member
This is great. Thank you Elvis for all the new information. I've read most van insulation posts on the Internet and they all contradict each other. But what you've explained makes the most sense to me. I'd still like to do some experiments for fun when I get some spare time.
I was already looking at that 48VDC A/C unit you mentioned. It's good to hear that others are using it. I'm just trying to figure out where the outdoor unit will fit.



I'm not sure how to create a 1/2" sealed air gap between the outer skin foil and the next foil layer. Would small blocks of wood or similar be acceptable to keep the second foil layer suspended? It will be difficult to accomplish in the cavities. I guess I'll have to figure that out when I get started.


For insulation I've decided to use something different. It's called semi rigid expanded insulation cork. It's basically super heated cork. This is different from typical cork in that there are no fillers and it has different properties. I'll use a range of thickness from 1/2" to 4". R-value is 3.6 per inch and it's okay for sound absorption/antivibration. I haven't found a performance chart at different temperatures yet but I'll ask the manufacturer.



I am reading a few books from the early 1900s about its application since it used to be very popular. Several companies sell it under different names these days such as Thermacork and Corktherm, but all from the same source in Portugal. It is a little expensive, but not too bad. I have a few samples and it seems like it will work. For hard to reach cavities I can crumble a few boards into granules and throw them in there. I guess I'll be the guinea pig on this one.
 
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Nomad_Elvis

Guest
I'm not sure how to create a 1/2" sealed air gap between the outer skin foil and the next foil layer.
Closed cell foam spacers.

The shape of the exterior sheet metal determines whether the gap is fairly uniform or irregular.

For fairly uniform gaps, you can even use TherMax, and there should be plenty of leftover scraps strips for that.

For irregular gaps, I'd suggest something along the lines of the Frost King black rubber foam tape found at home improvement stores, but that's just an example: the PSA on all their products is very low quality and you may need irregular shapes rather than strips. Rubber foams like the Aerocel foam Dave mentioned above will work. Almost everything to be glued on in an upfit needs very high grade adhesives, capable of withstanding high temperatures. Examples include 3M 80, 3M 90, DAP Landu Top & Trim High Heat Resistant Contact Cement. Exactly which one depends on the substrates. The DAP product is popular with auto trim shops because it works well with the type of foam & upholstery materials they use.

Spacers are only needed around the perimeter of any given cavity, with the interior sheet metal structure determining those boundaries.


For insulation I've decided to use something different. It's called semi rigid expanded insulation cork. It's basically super heated cork. This is different from typical cork in that there are no fillers and it has different properties. I'll use a range of thickness from 1/2" to 4". R-value is 3.6 per inch and it's okay for sound absorption/antivibration. I haven't found a performance chart at different temperatures yet but I'll ask the manufacturer. I am reading a few books from the early 1900s about its application since it used to be very popular. Several companies sell it under different names these days such as Thermacork and Corktherm, but all from the same source in Portugal. It is a little expensive, but not too bad. I have a few samples and it seems like it will work. For hard to reach cavities I can crumble a few boards into granules and throw them in there. I guess I'll be the guinea pig on this one.
Sounds like an unnecessarily expensive experiment with what is probably a not-commonly-available product used in an unproven application, in order to get about half the R-value per inch of alternatives available at Home Depot prices. A pragmatic person might ask the question, "Why?"

As for sound absorption, keep in mind that materials can have a good overall STC or NRC rating, indices that measure sound transmission/attenuation at frequencies outside of the problematical range in a motor vehicle, and not be ideal for use in a vehicle. A couple of useful references are attached.

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Graphite Dave

Dave Orton
Admittedly, given the cavities in the lower section of the Sprinter's side walls, flexible material would have to be a lot easier to put in place inside those cavities than rigid foam.

Aerocel looks a lot like Armaflex.
There are a lot of similar closed cell foamed rubber products designed for piping and duct insulation.
They are typically more expensive than some of the alternatives, but I have not priced Aerocel.

But the bottom line is only established when the cost is considered, so since you bought it, how much did it cost, for what thickness/size roll?

Since you bought it, do you have a weight per roll (for what thickness/size roll?)
Bought 1" Aerocel for $2.26/sq. ft. and 1/2" for $1.26/sq. ft. on 6-24-15

They come in 3' x 4' sheets.

Aeroflex contact adhesive cost $14.58/qt.

A sq. ft. of 1" thick weighs about 5 ounces.
 

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