MSA X-Large Filter Type H Hepa Optifilter Cartridge fits onto the motor/blower when the PAPR is used. Lightweight filter has an unrestricted air-inlet opening that helps to avoid gross debris from clogging the filter. It offers resistance to dusts, particles as well as mists and protects against a wide variety of contaminants. It is designed for Easy installation, thread directly to the cartridge receptacles on comfo and other twin-cartridges respirators.