Polytetrafluoroethylene (PTFE). It is composed of elastic materials such as compressed asbestos sheet, rubber, etc. and PTFE envelope cover. These are successfully used in chemical plants, glass/glass lines equipment due to their high temperature, corrosion resistance. These are used in areas where an envelope of pure PTFE is required to protect the exposed joint edge from corrosive attack or for applications where hygiene conditions are essential.