A foamed material constituting a thermal insulator (360) which comprises 50 wt % or more of a non-resin component, preferably 50 to 70 wt % of a mixture of cellulose, starch and a poly(vinyl alcohol). In a more preferable embodiment, the foamed material contains 30 wt % of cellulose, 25 wt % of starch and poly(vinyl alcohol 2C, 0.7 wt % of an antioxidant, 0.2 wt % of a mildewproofing agent, 0.2 wt % of a pigment and 43.9 wt % of a polyolefin resin (2), wherein the antioxidant is a phenol type antioxidant having a melting point of 110.degree. C. being lower than that of the polyolefin resin.