The invention relates to a process for generating a porous material having homogeneous, gas-containing inclusions in the micrometer and sub-micrometer range, and also to the material produced by such process.

The present invention relates to a method for producing a laminate, wherein the laminate is obtained by integrally laminating an expanded beads molded article (a) composed of expanded beads A and having interconnected voids and an expanded beads molded article (b) composed of expanded particles B and having interconnected voids, the difference [P.sub.bP.sub.a] between the voidage (P.sub.a) of the expanded beads molded article (a) and the voidage (P.sub.b) of the expanded beads molded article (b) is 5% or more, and the expanded beads A and the expanded beads B satisfy the following (1) to (3): (1) a difference [d.sub.Bd.sub.A] between an average hole diameter (d.sub.A) of the through-holes of the expanded beads (A) and an average hole diameter (d.sub.B) of the through-holes of the expanded beads (B) is 0.3 mm or more and 2 mm or less; (2) the expanded beads (B) have an average outer diameter D.sub.B of 3.5 mm or more and 5 mm or less; (3) a difference [D.sub.BD.sub.A] between an average outer diameter D.sub.A of the expanded beads (A) and an average outer diameter D.sub.B of the expanded beads (B) is 0.3 mm or more and 2 mm or less.

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.