PURPOSE: To obtain the title crosslinked foam having a smooth skin and closed cells at a low cost, by mixing chlorosulfonated polyethylenes having different Mooney viscosities at a specific ratio, adding a foaming agent, crosslinking agent, softener, etc., and continuously extruding, crosslinking and expanding the resultant mixture.

CONSTITUTION: The aimed crosslinked foam, obtained by adding a foaming agent (e.g., N,N'-dimethyl-N,N'-dinitroso-terephthalamide), a crosslinking agent (preferably magnesium oxide), a softener (e.g., chlorinated paraffin), etc., to a rubber component consisting of 30W70wt.% chlorosulfonated polyethylene having ≥90 Mooney viscosity and 70W30wt.% chlorosulfonated polyethylene having <90 Mooney viscosity, continuously extruding, crosslinking and expanding the resultant mixture, containing 3W6 pts.wt. crosslinking agent and 30W70 pts.wt. softener in 100 pts.wt. rubber component and having continuous smooth skin, closed cells, ≥4kg/cm2 tensile strength and preferably 0.1W0.6 apparent specific gravity.