It is the way in which a material (concrete, wood, paper…) will behave as a fuel. This reaction is defined after standardized tests in approved centers.
Extract CTS art. 8 “The roofing, the possible double interior roofing and the belt of the establishment must be made of materials of category M 2 whose report of classification in reaction to fire does not include a limit of durability (1).”
| Flammability | Examples | |
| M0 | non-combustible | stone, brick, cement, tiles, lead, steel, slate, ceramic, plaster, concrete, glass, rock wool, Staff |
| M1 | non-flammable | composite materials, rigid PVC, mineral slabs for false ceilings, some fireproofed woods, some fireproofed polyesters |
| M2 | hardly flammable | wall-to-wall carpeting, particle board |
| M3 | moderately flammable | wood (including glued laminate), rubber flooring, polyamide carpeting, wool |
| M4 | easily flammable | paper, polyester, polypropylene, mixed fiber carpet |
| NC | not classified |