Abstract: A thermoplastic resin having a Vicat softening point of 115.degree. C. or higher and containing a blowing agent is extruded and foamed into a foamed tubular body. The foamed tubular body is subjected to biaxial orientation and then pressed in antipodal directions, whereby the foamed tubular body is flattened and fusion-bonded at the resultant mutually-opposing inner walls thereof to obtain a foamed base material suitable for use in the fabrication of a car ceiling member. The foamed base material has not only excellent mechanical strength but also superb thermal strength. The foamed base material is not required to laminate films, sheets or the like thereon and is hence provided at a low cost.