Qorpak Green Thermoset Ribbed Cap with F217 PTFE Liner. These caps are known for providing the widest range of chemical compatibility and for being the most temperature tolerant of plastic closures. They also provide the most consistent adherence to close dimensional tolerances. Ideal for pharmaceutical applications. Thermoset closures cannot be remelted after they are formed. Common resins include urea, phenolic and melamine.