The Katadyn KFT Expedition No. 4 Replacement Element fits the Katadyn Expedition filter. The 0.2 micron silver impregnated ceramic filter removes silt, bacteria and giardia from the water, making it safe to drink. The silver quartz inside the filter prevents bacteria growth and recontamination. Leaves the water clean and tasting natural without using nasty chemicals. Bring this replacement element when you're off on a longer adventure or mission and you won't be near anywhere to get hold of a new filter.