Answer: the least flammable insulators are classified in the M0 category according to the French classification, and A1, A2 or B in the European classification, namely glass wool or rock wool for example.
Insulators must, for obvious reasons, have excellent fire resistance. In order to find your way around, a French classification is at your disposal, which classifies the insulators in five categories: M0 incombustible (the best), M1 flammable, M2 hardly flammable, M3 medium flammable, and M4 easily flammable. The level of classification will necessarily be marked on the product in store. There is also a European classification which follows the same logic, the best products being classified in class A1, A2 and B. The least recommended in categories C, D, E and F. The least flammable (and most ecological) insulators ) are glass wool and rock wool, as well as most mineral insulators.