Abstract: A high efficiency particulate air filter assembly (10) having low air flow resistance. The filter assembly (10) includes a radially pleated filter element (20) having a number of pleats generally equal to 14 times the numerical value of the diameter in inches plus 5 times the numerical value of the diameter divided by the square root of the pleat height, thus ##EQU1## The filter element (22) is mounted within a canister shell (24) having an end face (42) so designed that a negative fit test may be readily performed.

Abstract: A sorbent type filter assembly (10) which is made by sequentially placing a first resilient perforated plate (40), a first retention filter (36), a sorbent bed (34), a second retention filter (38), a second resilient perforated plate (42), and a cover (14) within the cylindrical portion (16) of a canister shell (12). The cover (14) is forced downwardly to compress the sorbent bed (34) and to resiliently spring bias or stress the first resilient perforated plate (40). While the parts are held together under compression, an annular edge portion of the cylindrical shell is rolled into a circumferentially extending groove on the canister cover to hermetically and mechanically hold the parts together in their assembled and compressed relationship.