These need to be used on top of the gas and vapour cartridges using a filter retainer and will then give gas, vapour and dust protection. 5925 is a P2 filter with an assigned protection factor of 10 (APF 10) and 5935 is a P3 with an assigned protection factor 20 (APF 20, APF 40 on full face mask). Filter 501 retainer also available. (EN143/CE marked). Filters are supplied in packs of 10 (5 pairs). Filter retainers sold as pack of 2.