Ammonium hydrogen fluoride is a compound formed from ammonium fluoride and hydrogen fluoride, with hydrogen fluoride molecules occupying spaces in the ammonium fluoride crystal lattice. It is the major constituent in glass-etching fluid (though sometimes replaced by potassium hydrogen fluoride), etching occurring due to the fluorination of silicon:
SiO_{2 (s)}+ 4[NH₄][HF₂] _(aq) SiF_{4 (l)} + 4[NH₄]F _(aq) + 2H₂O _(l)

Bifluorides are considered toxic although they are not well characterized. Potassium bifluoride is not listed in the TSCA (Toxic Substances Control Act) inventory on the US. They are all considered irritating to the skin and lungs and toxic by inhalation.

Oxygen difluoride was first reported in 1929; it was obtained by the electrolysis of molten potassium fluoride and hydrofluoric acid containing small quantities of water.[2][3] The modern preparation entails the reaction of fluorine with a dilute aqueous solution of sodium hydroxide:
2F₂ + 2NaOH OF₂ + 2NaF + H₂O