Soft Char

These intumescents produce a light char which is a poor conductor of heat thus, delaying heat transfer. Ablative coatings, for example, contain a significant amount of hydrates. When the hydrates are heated, they decompose and water vapour is released, which has a cooling effect. Once the water is spent, the insulation characteristics of the char that remain can slow down heat transfer from the exposed side to the unexposed side of an assembly.

Soft char products are typically used in thin film intumescent coatings for fireproofing structural steel as well as in firestop pillows. Typically, the expansion pressure that is created for these products is very low, because the soft carbonaceous char has little substance, which is beneficial if the aim is to produce a layer of insulation.