Features: This is Respro,s new polymer seal, the PRO-SEAL® It provides an even better seal to your Respro® mask The PRO-SEAL® can be retroactively fitted into any Respro® mask no matter when you bought it, last week or 23 years ago It provides improved sealing which reduces inward leakage Inward leakage (IL) is unfiltered air that gets in around the sides of a mask and filter because a mask fits poorly or just doesn,t make a proper seal (think ear loop masks) The PRO-SEAL® helps keep the filter away from the face which in turn increases the over all surface area of filter material to draw air through which not only reduces inhalation resistance, but makes it easier to breathe through and a more comfortable experience The PRO-SEAL® is more compliant and accommodates a wide range of face shapes