This is the catalyst for FC21 Flat Clear, mixed at a 6:1 ratio (clear : catalyst). FC21 Urethane Flat Klear is a low VOC, flat-finish clearcoat that can be used over all solvent-based basecoats — it sprays easily and dries quickly, and just needs to be mixed with the KUF21 catalyst to be ready to spray. It’s coast-to-coast VOC compliant for use in all states, and is specifically formulated to work only with FC21 Flat Klear.