A late search for a bit more information. I want to make the Penz filter referenced early in this thread. Would it make a big difference if I use a canister manufactured in the usual way where the air flows from the inside outwards. The reason is the shipping from Wynn Environmental to my home in Canada is almost as much as the cost of the canister and therefore doubles the cost. I can get canisters locally made with the usual air flow direction. Thank you.