The substance is applied as a separate layer (surface treatment) or impregnates the product throughout (medium and deep). Depending on the chemical composition, the material reacts differently to heat. Usually, several components are included in the fire retardant, which comprehensively protect the wood:
- Decompose with the absorption of a large amount of heat. The burning zone cools down, and the wood chars only with forced intense flame treatment.
- Expand (increase in volume multiple times). Fire-resistant foam appears on the surface, providing thermal insulation for the wood underneath. The foam restrains the spread of fire.
- Release non-combustible gas. Oxygen is displaced, and the flame becomes less intense or extinguishes. After treatment, wood ignites more slowly, does not sustain combustion — the "activation" of protection stops or slows down the spread of fire.