Hydrogen fluoride is a chemical compound with the chemical formula HF. This colorless gas or liquid is the principal industrial source of fluorine, often in the aqueous form as hydrofluoric acid, and thus is the precursor to many important compounds including pharmaceuticals and polymers (e.g. Teflon). HF is widely used in the petrochemical industry and is a component of many superacids. Hydrogen fluoride boils near room temperature, while other hydrogen halides evaporate at much lower temperatures. Unlike other hydrogen halides, HF is lighter than air and diffuses relatively quickly through porous substances.