Long lengths of a heat-shrinkable sleeve for use in splicing electrical cables are made in a continuous process. The sleeve 10 is formed round a permeable core into which fluid is introduced under pressure to expand the sleeve radially when heated. The core and sleeve are advanced together axially first through induction heater 40 then through heating pipe 56 followed by conical section 60 wherein the sleeve expands while hot lubricating fluid circulates through 56, 60. The sleeve and core then pass through cooling region 64 wherein circulating cooling medium is spaced from sleeve 10, followed by cooling region 66 where the medium contacts sleeve 10. After drying the material is wound on drum 90. Finally, the core is removed and the sleeve cut into lengths. The sleeve may include a stress graded compound made by heating a dimethyl silicone liquid to remove gas and mixing the liquid with a silicone carbide powder capable of passing through a 400 mesh screen, the volumetric proportion being 1 part liquid to 0.5 to 2.0 parts powder.