The present invention relates to paper or paperboard comprising cellulose fibers, said paper or paperboard comprising at least one coating layer formed by extrusion coating of a PP (polypropylene) resin, characterized in that the PP resin comprises at least 50% by weight of a branched PP copolymer having a density in the range of 890-910 kg/m.sup.3 (as determined according to ISO 1183), a melting temperature in the range of 155-170 C. (as determined according to ISO 11357-3), and a melt flow rate (230 C./2.16 kg) in the range of 10-15 g/10 min (as determined according to ISO 1133), and wherein the PP resin is applied to the paper or paperboard at a grammage of less than 30 g/m.sup.2.

A thermoplastic resin foam including a thermoplastic resin, wherein: the thermoplastic resin includes a polyester resin and a polyimide resin, and the thermoplastic resin foam shows a single glass transition temperature Tg. The glass transition temperature of the thermoplastic resin is preferably 80 to 130 C. An absolute value of difference between heat absorption and heat generation, each determined by heat flux differential scanning calorimetry at a heating rate of 10 C./min, is preferably 3 to 35 J/g.