To obtain the subject material having excellent heat resistance, a large expansion ratio, and a low specified gravity and also having a tackiness on the surface, and useful as a sealing material by using ethylene-propylene based copolymer rubber as a rubber component.

This expanded material is obtained by expanding and crosslinking a rubber composition containing (A) an ethylene-α-olefin based copolymer rubber, (B) an organic peroxide and (C) a forming agent (preferably azodicarbonamide) in a hot air. A specific gravity of the objective expanded material is ≤0.2 and the component A is ethylene-α-olefin copolymer rubber or ethylene-α-olefin-nonconjugated diene copolymer rubber and especially the α-olefin is propylene and the nonconjugated diene is 5-ethylidene-2-norbornene or dicyclopentadiene, and preferably the component B is contained in an amount of 0.5-25 pts.wt. and the component C is contained in an amount of 3-53 pte.wt. to 100 pts.wt. of the component A.