Is spray foam heat resistant?

The sheets call it temperature resistance, heat resistance or thermal resistance after curing, and none of them names a test method. It is the range the cured foam is meant to stay in once it is in place, a different number from the 41 to 86 F the cans have to be sprayed at and from the 122 F a full can must never be stored above.

Some documents disagree. TYTAN’s Thermospray sheet gives -40 to +90 C on one page and -200 to +240 F on the next, which are not the same range, and Kraken Bond’s black foam has a straw-can sheet at -103 to +239 F and a gun-can sheet at -40 to +176 F. The tables print both.

Fire block foams are sold on how the foam burns, as a surface-burning result or a fireblocking listing, not on the heat it takes in service. Their cured-foam ceilings run from 194 to 240 F, no higher than the gap fillers at 176 to 240 F, so a fire block can is not the answer to a hot spot.

Two names point the wrong way. Stanley’s F952P is listed on Amazon as heat resistant, and its sheet prints +194 F, lower than the plain F952 at +239 F. The 113 in TYTAN Fire Block 113 is not a heat rating either: its sheet gives the cured foam the same -200 to +240 F as TYTAN’s other foams.

Only a few documents say where foam must not go. DuPont’s Froth-Pak sheet says cured foam is combustible and will burn if exposed to open flame or sparks, and that it should not be sprayed where it can touch hot surfaces such as heaters, furnaces, fireplaces or recessed lighting fixtures. Loctite keeps its gap filler away from chimneys, heater vents and steam pipes, or anywhere the surface can pass 187 F, and HandiFoam says its foam will support combustion above about 240 F.

The ranked one-component kit sheets say nothing about chimneys, flues or recessed lights, and BEEST’s guide only warns against heat sources and open flames while you spray. The FastCoat and ThermCoat manuals list pipes and HVAC ducts among the uses without a temperature limit, so the label of the product you bought and the clearances your code sets are what decide a job near a flue.