Thermwell Products 4 Pack 3' Black Tubular Polyethylene Foam Pipe Insulation. This non self-sealing, pre-slit insulation with a 1/2" wall thickness is designed for use on 1/2" copper pipes or 1/4" iron pipes. It effectively helps save energy when used on hot water pipes and prevents cold pipes from condensation. The pre-slit seal allows for easy slipping over pipes, making installation a breeze.