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Comparative flammability of EPS, XPS, and polyiso rigid foam

bluesolar | Posted in Green Products and Materials on

Hi all — Do EPS, XPS, and polyiso have different fire characteristics? Are any of them more or less flammable than the others?

I’ve been unable to find clear information on this on the web. I do find sources that state that EPS is not very flammable, including this video demonstration by ThermaSteel:

A lot of the rigid board products claim to be “fire rated”, but it doesn’t seem to mean much since building codes still requires a barrier like drywall for them.

Dow/DuPont came out with a polyiso board product – Thermax – that claims to be unusually flame resistant and can be used without a barrier (in the US at least). But it doesn’t seem to be sold anywhere. (What is it with Dow making it so hard to give them money for their products? They made it similarly hard to get their brilliant solar shingles – Powerhouse – and ended up selling the technology to RGS. What a strange company…) Here’s more on Thermax:

Thanks for your input.

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  1. jasonhoetger | | #1

    A bit late to the party, but in case you're still looking for information on alternatives to hard-to-find Thermax, I found this report on other types of polyiso that don't require thermal barriers:

  2. severaltypesofnerd | | #2

    Halo products Graphite polystyrene (GPS) claims to not require a fire barrier layer.... passing NFPA 286 by itself....

  3. severaltypesofnerd | | #3

    The foam haters hang out at:
    A blog on foam and fire.

  4. rockies63 | | #4

    I'm always surprised when people answer a question about a particular aspect of a product but never ask what it's going to be used for.
    Is this foam going to be used on the interior or exterior of a building? Are you interested in the thermal performance of the foam as well as the fire rating?
    Personally, if fire is a concern, especially if you are in a wildfire interface zone, I would go with Roxul Comfortboard on the exterior and Roxul Comfortbatt within the wall cavities. This product is definitely not flammable at all.

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