Definition - What does Intumescence mean?
Intumescence is the occurrence where a substance increases in size when exposed to a significant increase in temperature. It is typically used by fire safety personnel as a passive fire protection mechanism to indicate the potential existence of a fire. Substances used for intumescence increase in size and decrease in density, a quality that is used in containing the spread of a fire.
Corrosionpedia explains Intumescence
Intumescence is applied in the use of passive fire protection devices. Such devices are fire-resistant doors, walls or glass. It is classified based on the type of char produced when exposed to heat. There are two main types of intumescence: hard and soft. Soft char reduces heat transfer by being a poor conductor of heat, while hard char is produced with graphite and used for external fire-proofing.