In strictest terms, calcium silicate boards refer to autoclaved flat boards consist of calcium silicate hydrates crystallized under the form of Xonotlite, Ca₆Si₆O₁₇(OH)₂, reinforced with cellulose fibers, having density not more than 800kg/m3. There are various types of calcium silicate boards, with different selected special additives and densities (from 450kg/m3 to 800kg/m3). With very good fire resistant, fairly good impact resistant and moisture resistant properties, they are widely used as fire protection lining boards in fire rating floors - partitions - ceilings - roofs - beam and column encasements in buildings, tunnels, ocean vessel interior, etc.

Autoclaved flat boards consist of calcium silicate hydrates crystallized under the form of Tobermorite, chemically known as Ca₅Si₆O₁₆(OH)₂.4H₂O, reinforced with cellulose fibers, with densities ranging from 1000kg/m3 to 1800kg/m3, are called̀ autoclaved fiber reinforced cement flat boards. Common features of these products are non-combustible, fire resistant (though far poorer compared to calcium silicate boards), high impact resistant, high moisture resistant, in some products, even immune to permanent attack from sun lights and rains, dimensionally stable under the temperature and moisture effects of surrounding environment. For products of similar production technology, the heavier in density, the stronger in impact and water resistance; but the weaknesses are difficult for transportation and handling during installation. Autoclaved fiber reinforced cement flat boards are used in various applications for floors - walls - roofs - ceilings - lost formworks (lining boards for reinforced concrete structures during concrete pouring) in all types of building construction.