Abstract: There is provided a pre-expanded particle having a high expansion ratio and excellent flexibility and cushioning property. The in-mold articles made thereof do not lose mechanical strength, heat resistance, and water resistance, without conventional volatile organic foaming agents or carbon dioxide gas. A pre-expanded particle of a polypropylene resin is prepared by pre-expanding a water-containing propylene resin composition comprising (A) 100 parts by weight of a polypropylene resin having melt flow rate (230° C., 2.16 kg load) of 10 to 70 g/10 min and tensile elongation at break of at least 300%, (B) 0.05 to 10 parts by weight of a hydrophilic polymer and (C) 0 to 3 parts by weight of a filler and having a water content of 1 to 20% by weight under a water vapor pressure at the melting point of the polypropylene resin, said particle having an apparent expansion ratio of 25 to 70 times, a closed cell content of at least 85% and an average cell diameter of 50 to 500 &mgr;m.

Abstract: Heat temperature at the expansion molding of a finished expanded article is decreased by lowering the melting peak temperature of the pre-expanded particles of a polypropylene resin. Comprising the polypropylene resin and a .beta.-crystalline-nucleating agent, the percentage of the .beta.-form in the whole crystalline region is 5 to 100 parts by weight.