But polyisocyanurate sheet is not usually recommended for use in ICFs. Because they contain cement, the composite materials tend to be strong, heavier than the pure foams, possibly more durable, and require somewhat more effort to cut and shape. Their insulating value is a bit lower. Cost estimates are unavailable since the material comes only in completed, molded units. All of the plastic foams are highly inert.
None is considered toxic by U.S. government agencies.
None contains any formaldehyde. None has been linked to respiratory problems or skin irritation, as have some fiber-based insulations. Attempts to find any emissions from polystyrene foams used in walls failed. No emissions could be detected by the most sensitive instruments. The plastic foams used in ICFs are also formulated so that they do not burn by themselves.