a method for manufacturing a gas mask canister using a hepa filter media having plastic separating plates inserted into between hepa filter media at certain intervals . the hepa filter , impregnated activated carbon , and a pre - filter are accommodated within a cylinder . the cylinder is inserted into a canister having an upper portion and a lower portion detachably coupled together . the impregnated activated carbon , the plastic separating plates and the casing of the canister can be reused , and the rest of elements are burned . a vinyl coating sheet is peeled off from the canister after each use . an indexing tab for recording the number of times of peeling is attached on each of vinyl coated sheets , so that the number of uses can be known .