Abstract: A polyester film for printed circuits to be used as a base in a printed circuit base plate or as a base and/or cover layer in a printed circuit board, which undergoes a degree of dimensional stability of not more than 1% in both the longitudinal and transverse directions when kept at 150.degree. C. for 30 minutes, and which is obtained by heat treating an extrusion molded and stretched polyester film at 150.degree. C. to 240.degree. C. without applying tension.

Abstract: A material for reinforcing a panel or plate includes a first resin layer having a high tensile modulus of elasticity after hardening; a second resin layer having a low tensile modulus of elasticity after hardening; an expandable member disposed between the second resin layer side and the panel to be reinforced. The expandable member is narrower than the reinforcing resin sheet. The first and second resin layers are combined in an unhardened or semi-hardened state to form a reinforcing resin sheet. The expandable member expands into a bead-like projection when heated and then hardens. The edges of the reinforcing resin sheet extend beyond the edges of the bead-forming member or expandable member is such a manner that the second resin layer of the reinforcing resin sheet can be attached to the panel or plate.