It is composed of polystyrene foam and specially formulated pressure activated adhesive. Suitable for Plastic, glass or metal containers all available. For excellent adhesion to the lip of plastic and glass container, foam thickness and torque are very important. it do not need to be seal, you just insert the seal into the closure and screw the lid up. When you take off the lip, it was sealed with bottle together, and there isn't any heating machine sealing.