Abstract: A snap-on filter for chemical cartridges is presented which includes a filter element comprising a perforated fiberglass prefilter bonded to a felt filter. The filter element is contained within a filter housing which snaps onto the chemical cartridge of a standard gas mask. The fiberglass prefilter is perforated to provide a passage way for fumes into the interior of the filter as well as the filter surface. The perforations increase the overall surface area of the prefilter for filtration. This feature enhances the efficiency and overall life of the filter element.