Black Phenolic F217 & PTFE Lined Caps are known for providing the widest range of chemical compatibility and for being the most temperature tolerant of plastic closures. Foam backed PTFE liners resist attack from virtually all chemicals at room temperature and provides resilience for a tight seal with a low moisture transmission rate. F217 has a low density foam core between two solid layers of LDPE. Uses include analytical lab samples, high purity chemicals, strong acids solvents, environmental samples, pharmaceuticals, and diagnostic reagents.