Black Phenolic F217 & PTFE Lined Caps are known for providing the widest range of chemical compatibility. 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.