ETI Duct tape,sometimes called duck tape, is cloth- or crim-backed pressure-sensitive tape, often coated with polyethylene. There are a variety of constructions using different backings and adhesives. Duct tape is heat-resistant foil (not cloth) duct tape useful for sealing heating and cooling ducts, produced because standard duct tape fails quickly when used on heating ducts. ETI Duct tape is silvery gray in colour.