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Community and Q&A

Polyethylene foam as insulation

smoojee | Posted in Green Products and Materials on

Hi! I’m beginning a new project building out a small camper van for use in cold climates primarily. Because its a small space I’m extra concerned about the safety / toxicity of materials that I’m using. The walls of the van are aluminum so condensation in cold climates is going to be a real issue. I know that laying some type of insulation that doubles as a vapor barrier is my best option to preventing any sort of mold issues. However, when looking at my options for materials I’m not thrilled. Most of the foams used in the building industry from XPS, Polyiso, etc. seem to have questionable health safety red flags in terms of offgassing or fire retardant additives. More eco friendly options such as wool, or denim don’t solve the vapor permeability issue…

I have come across polyethylene foam though as a potential option however (the kind of foam used to make swim noodles) and I was wondering if anyone had any positive or negative experiences with the material or maybe knows something I don’t regarding its suitability as insulation or potential toxicity issues I have overlooked.

If polyethylene doesn’t work, I will probably go with expanded cork insulation….expensive, but affordable due to small dimensions of space I am insulating.

Thanks to any and all who have any input regarding this!

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  1. GBA Editor
    Martin Holladay | | #1

    Polyisocyanurate does not include worrisome fire retardants and isn't manufactured with environmentally damaging blowing agents. I have never heard of any offgassing complaints about polyiso.

    For more information, see "Choosing Rigid Foam."

  2. smoojee | | #2

    Hi Martin,

    Thank you for the response. I have looked further into polyiso and while it seems it is the best option of the commonly found insulation foams, my concern is that this small aluminum campervan will be used in areas with temperatures that will routinely drop below zero. Polyiso's R-Value seems to take a big hit in lower temperatures and I'm limited by size to about 1.5 to maximum 2 inches of insulation.

    EPS or XPS perform much better in cold climates but the questionable safety of blowing agents and fire retardants has me concerned.

    This has left me searching for other options.

    As far as natural options go, expanded cork seemed like a good option but has a perm rating greater than 2.0 for one inch. I'm concerned with condensation forming between aluminum walls and insulation. Although any moisture that does form would not be trapped by insulation and could evaporate it would decrease r-value significantly by increasing conductivity of insulation.

    This has led me to search for potential other foams. Either XPS or EPS without fire retardants or other closed cell foams like polyethylene. or Volara

    both of which seem like good options. I'm just curious why these other foam types haven't caught on as building insulation? I'm apprehensive to try a product that could potentially fail although they seem like a better option than whats traditionally found in big box home improvement stores.

  3. smoojee | | #3

    Continuing research, what exactly is the downside to using EPS without any flame retardant?

    Although burning EPS gives off black smoke, the
    toxicity of the released smoke fumes is considerably less
    than those of other commonly used materials. This was
    already concluded in 1980 by the TNO Centre for Fire
    Safety14 for both EPS in its standard design and EPS
    to SE quality. The toxicity of fumes was measured for
    wood, wool, silk, cotton, fire retardant treated cotton
    and three sorts of EPS (see table). In the case of EPS the
    toxicity of the smoke appeared to be considerably
    smaller than that of the other materials. (

    I can purchase EPS through a foam supplier in sheets. It will be faced with another material...most like 1/8 inch plywood so it will be proctected from sparks etc....and if it does go up in flames it would burn of quickly and would release less toxins it seems than most other materials.

  4. Jon_R | | #4

    Polyethylene foam is what, R3? Consider Dow Thermax, which retains its R value when cold.

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