Duct tape or duck tape is cloth- or scrim-backed pressure-sensitive tape - often coated with polyethylene. There are a variety of constructions using different backings and adhesives. One variation is gaffer tape - designed to be cleanly removed, unlike standard duct tape. Another variation is heat-resistant duct tape useful for sealing heating, ventilation and air-conditioning ducts, produced because standard duct tape fails quickly when used on heating ducts. Duct tape is generally gray or black but also available in other colors.