Heat Transfer Mask is used to transfer heat transfer media to the garment, such as printed pattern HTV as well as printable transfers like StarCraft Transfers for Dark Materials. Regular HTV such as Siser EasyWeed comes with it's own Heat Transfer Mask (also called a carrier sheet) so this is not required for those products. Since the surface has to be exposed on custom printed pattern vinyl for us to print on it, the heat transfer mask is not applied like it is on a product like Siser EasyWeed HTV. Heat Transfer Mask is usually reusable at least 2-3 times depending on how clean you are able to keep it. The more it looks it's sticky tack, the more difficult it will become to reuse.