Intumescent

[Julene]

Substances which swell as a result of heat exposure thus increasing in volume and decreasing in density. Intumescents are typically endothermic to varying degrees, as they can contain [chemically] bound water. Intumescents are used in firestopping, fireproofing and gasketing applications. Some intumescents are susceptible to environmental influences such as humidity, which can reduce or [negate] their ability to function. DIBt approvals [quantify] the ability of intumescents to stand the test of time against various environmental exposures. DIBt approved firestops and fireproofing materials are available in Canada and the US. DIBt approvals have a [finite] validity and one must check the expiry date, which is printed on the front of the approval document.

[Britney]

(of a coating or sealant) swelling up when heated, thus protecting the material underneath or sealing a gap in the event of a fire.