The definition “intumescent” indicates that the material has an expanding capability when exposed to fire or heat. Intumescent materials are used on penetrating materials that would burn or melt away during a fire such as plastic pipes, low melting materials (eg combustible insulation) or cables.
Even in cases where the penetrants do not burn or melt, intumescent materials offer the advantage of being able to expand and seal many cracks or gaps that may have developed or be the result of improper installation.
Do not be confused with "endothermic", which are products that block heat by chemical absorption and moisture release.