OV (organic vapor) cartridges with P95 prefilters feature a removable clear prefilter cover that helps retain the prefilters while also making it easier to do a fit check on the cartridges once attached to the respirator. The OV cartridges are long life, while the P95 prefilters are oil resistant, so they don't need to be replaced after each shift unless they are hard to breath through due to filter loading. Cartridges feature bayonnet fittings for easy attachment and consistent fit on the respirator body. Meets NIOSH requirements (National Institute for Occupational Safety and Health).