Is there any danger of bad fumes/gasses being released from polyisocyanurate or polystyrene rigid foam insulation? I'm planning on insulating my bedroom from the inside (ie: putting the insulation between the studs), and I'm wondering if I need to worry about fumes over the years.

My guess is there's no issue, as people use this stuff all the time, and my vapour barrier will prevent any air movement anyway. Still, it was brought up by a hardware store I called, so I'd like some sanity-checking opinions.

Edit: Since I've been able to find precious little information on insulating the inside of exterior walls with rigid insulation, I've decided to go with Roxul (fibreglass-ish) insulation instead.

To answer my question though, I've asked people IRL, and they pretty much scoffed at the idea that rigid foam insulation gives off fumes.

  • the stuff if pretty nasty if it burns, but is a common insulation material for all sorts of approved uses. BTW, you don't want to use foam insulation AND a vapor barrier. Foam insulation is typically considered the vapor barrier.
    – DA01
    Jul 3, 2012 at 22:55
  • 1
    Ya, I've heard it's nasty, and code requires it be covered by a fire barrier - drywall suffices. From what I've read, foam insulation is a vapour retardant (if I'm using the right terminology), not an outright barrier. I'm getting conflicting reports about foam & VB, so I'm going to ping a local contractor. Nonetheless, thanks for your reply DA01 - not the first I've valued today. Jul 3, 2012 at 23:02
  • Foam insulation could be a vapor barrier if it is continuous but pickle will be cutting it into 14.5" pieces and putting it between the studs. There will be lots of gaps between the hand cut foam and the irregular wood studs. Jul 4, 2012 at 17:05
  • The two answers so far illustrate the gulf between the manufacturer's stance and the viewpoint of those concerned with indoor pollution, many of whom suffer from various hypersensitivities. You'll end up deciding for yourself if this will be tolerable to you. A well installed vapor barrier will help significantly if the outer wall materials allow the gases to escape in that direction.
    – bcworkz
    Nov 27, 2012 at 19:41

5 Answers 5


According to the Material Safety Data Sheet (MSDS) for TRYMER(TM) 3000 Rigid Polyisocyanurate Insulation, there should be no problems (for this specific product anyway).

I also found the MSDS of an example Expanded Polystyrene Board, which does mentions off-gas issues. Though it only applies to large amounts of "fresh" polystyrene, being stored in a "confined, unventilated area".

fresh polystyrene contains residual pentane and if large amounts of EPS materials are stored in a confined, unventilated area such as a semi-trailer truck, pentane may off-gas and create measurable airborne concentrations.

If you know the specific product you'd like to use, it shouldn't be that difficult to find the MSDS for it on the internet.


Yes, foam board offgasses. All plasics, some woods (pine), wood products, paints and adhesives do. Some offgas products are more of a concern than others. For example, the formaldehyde emanating from OSB, MDF, particle board and plywood is perhaps the single greatest hazard in North American homes today. It has long been associated with increased risk of asthma and cancer. Our new super-insulated home has none of these wood products and our last home, also processed-wood product free, sold above market value because it was so free of contamination.

Foam board releases small amounts of brominated flame retardants, and this is a serious concern. I personally would not use foam board indoors. Having said this, flame retardants are in damn near everything: all upholstery materials, draperies, mattresses, carpets.....I'm finding this to be even more difficult to eliminate than formaldehyde. The fact is, most of us are exposed to more danger breathing in our own homes than outside in our polluted cities.


Styrene is reasonably anticipated to be a human carcinogen based on limited evidence of carcinogenicity from studies in humans, sufficient evidence of carcinogenicity from studies in experimental animals, and supporting data on mechanisms of carcinogenesis. [...]

Polystyrene is used extensively in the manufacture of plastic packaging, thermal insulation in building construction and refrigeration equipment, and disposable cups and containers. Styrene polymers and copolymers are also increasingly used to produce various housewares, food containers, toys, electrical devices, automobile body parts, corrosion-resistant tanks and pipes, various construction items, carpet backings, house paints, computer printer cartridges, insulation products, wood-floor waxes and polishes, adhesives, putties, personal-care products, and other items, and they are used in paper processing (IARC 2002, Luderer et al. 2005, NLM 2008).

–National Toxicology Program; Report on Carcinogens, Thirteenth Edition (styrene.pdf)


I am a Remedial Timber and Damp Surveyor. We also insulate houses as part of our services. To answer the question if PIR Insulation can also be a Vapor Barrier the answer is yes provided it has aluminum foil bonded to both surfaces. When you fit this flush between your timber studs, tape the joints between the insulation and the timber stud with aluminum tape ensuring all the timber is covered. You would also need to ensure that the joints between the insulation and the walls, ceiling and floor are sealed.


Owens corning states that extruded foamboard is not a vapor barrier in itself as it has a permiability rating of 1.1. Strandboard for example has a lower rating of 0.7. So even taped foamboard needs a plastic film vapor barrier. Put the barrier on the inside of the house side and staple/tape it so that the foamboard will only offgas to the outside. (yes the free styrene-a kind term for vinyl benzene will offgas but not as bad as sprayed foam) -from a construction guy with a severe MCS wife.

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