Triflic acid, the short name for trifluoromethanesulfonic acid, TFMS, TFSA, HOTf or TfOH, is a sulfonic acid with the chemical formula CFSOH.  It is one of the strongest known acids. Triflic acid is mainly used in research as a catalyst for esterification. It is a hygroscopic, colorless, slightly viscous liquid and is soluble in polar solvents.