To protect the engine in very wet conditions, Twin Air designed a special Rain Coat (RC). The Rain Coat is an extra filter cover. During these extreme wet weather conditions, we advise to use the pre-oiled Twin Air filters, pre-oiled with Liquid Bio Power Filter Oil and on top of that mount the dry Rain Coat. HONDA CRF250R 18-19 CRF450R 17-20 CRF250RX 19- CRF450RX 17-20