Bottle cap liners, which sit between a cap and the bottle, are manufactured for many specialized purposes, including providing chemical resistance, acting as moisture barriers and preventing leakage. The primary function of a bottle cap liner is to properly seal a bottle, making chemical compatibility highly important. Vinyl-lined caps are suitable for medical and chemical applications, including mild acids, alkalis and solvents, as well as alcohols and oils. PTFE-lined caps are resistant to attack from virtually all chemicals at room temperature, while rubber lined caps are autoclavable and resistant to moisture vapor with relatively low gas transmission. Polyethylene lined caps are suited for non-oil products filled at room temperature and offer a low moisture vapor transmission rate and good chemical resistance.