Semi-Slit Pipe Insulation for Plumbing Pipes, Copper and PEX Tubing, or HVAC lines : half-slit for slide-on application ; can be split open if needed for existing lines ; Polyolefin foam insulation is available in a wide variety of sizes and styles. PE foam insulation is non-porous, non-fibrous and resist mold growth. It is completely recyclable and cost effective.