Perfluorobutanesulfonic acid (PFBS) is a chemical compound with a four carbon fluorocarbon chain and a sulfonic acid functional group. As an anion it functions as a stable fluorosurfactant because of the strength of carbon–fluorine bonds. Since June 2003, 3M has used PFBS as a replacement for the persistent, toxic, and bioaccumulative perfluorooctanesulfonic acid (PFOS) in its Scotchgard stain repellents. 3M markets surfactant with PFBS in two fluorosurfactants.