Most fabric softeners are designed for addition to the rinse or drying cycles, but a few are available for the wash- and rinse-added types are liquids; dryer-added fabric softeners come as sprays, impregnated tear-off sheets, and impregnated foam (porous) sheets, or as a slow dispensing solid bar that attaches to the fin of a dryer.  The softening agents most commonly used are cationic quaternary ammonium compounds.  Bluing is frequently included, as well as fragrance.  Infrequently, antimicrobial ingredients or fluorescent whitening agents are added.  Fabric softening ingredients also are incorporated in some laundry detergent products.