An inorganic-organic composite comprises an inorganic phase, such as gypsum crystals, and a film forming organic phase. The film forming organic phase is selected from substituted starches having a degree of polymerization; degree of substitution and viscosity such that the substituted starches are insoluble in water during mixing but dissolve at a higher processing temperature during forming, setting or drying of the composite. Thus, excessive migration of the substitute starch is prevented and the composite is substantially strengthened.