Hydrofluoric acid (HF) is a solution of hydrogen fluoride in water. Hydrofluoric acid is a highly corrosive acid, capable of dissolving many materials, especially oxides. Because of its high reactivity toward the glass and moderate reactivity toward many metals, hydrofluoric acid is usually stored in plastic containers (although polytetrafluoroethylene is slightly permeable to it).
Hydrofluoric acid attacks the silicon oxide in most types of glass. It also dissolves many metals (not nickel or its alloys, gold, platinum, or silver), and most plastics. Fluorocarbons such as Teflon (TFE and FEP), chlorosulfonated polyethylenene, natural rubber, and neoprene all are resistant to hydrofluoric acid. Hydrofluoric acid is so corrosive because the fluorine ion is highly reactive. Even so, it is not considered a 'strong' acid because it does not completely dissociate in water.