Foamed thin materials such as foamed film and foamed fibrillated materials produced by extruding a composition consisting of 100 parts by weight of aliphatic polyester having a melt viscosity of 1.0.times.10.sup.3 -1.0.times.10.sup.5 poises at a temperature of 190.degree. C. and a shear rate of 100 sec.sup.-1, and having a melting point of 70.degree.-200.degree. C., and 0.2-5 parts by weight of foaming agent. These foamed thin materials has biodegradability, excellent mechanical, insulating, touch and aesthetic properties. They are useful materials as insulating, packaging, oil absorbing materials and filters.