Abstract: A chlorinated polyolefin composition suitable for use in the manufacture of crosslinked, thermoset, flame-retardant articles such as jackets for electrical or fiber optic cables and heat-shrinkable tubing for protection of cable connectors and splices. The composition is thermosetting and moisture curable and comprises a chlorinated polyolefin such as chlorinated polyethylene or chlorosulfonated polyethylene and a non-chlorinated polyolefin which contains moisture crosslinkable silane groups. The non-chlorinated polyolefin preferably comprises polyethylene or a copolymer thereof. Exposure of the composition to moisture causes the formation of intermolecular crosslinks between molecules of the non-chlorinated polyolefin. The compositions can be formed by blending the non-chlorinated polyolefin with a silanated non-chlorinated polyolefin or by silane-grafting a blend of the chlorinated polyolefin and the non-chlorinated polyolefin.