PURPOSE: To provide a thermoformable composite material not largely changed in the bonding strength of an inorg. fiber and a thermoplastic resin core material at the time of the reheating in the case of thermoforming or at the time of molding and not generating the lowering of strength.

CONSTITUTION: A thermoformable composite material is obtained by a laminating process superposing polyolefin resin films containing a silane crosslinked polyolefin resin on both surfaces of a nonwoven mat-like article based on inorg. fibers subjected to needle punching treatment to form a laminate, a heating process heating the laminate at temp. equal to or higher than the m.p. of the resin component of the laminate to melt the resin component, a compression process compressing the heated laminate to infiltrate the resin component into the nonwoven mat-like article and an expanding and opening process expanding and opening the laminate in a resin component impregnated state to increase the thickness of the laminate.