While i was browsing for free flowing air filters, i happened upon this link that mentions the correct way of cleaning foam type air filters. This is interesting because our tuning shops(atleast where i go) simply use a blower to rid the foam of dirt and then pop the filter back in the filter box. Here's the correct procedure:
On Oiled Foam filters the real filter is the oil. The foam is only a support for the oil. Sort of like a skeleton. You must oil the foam on these filters. If you do not, the filter will not work ! To clean them, rinse in solvent several times or until clean. Then ring them out, and let them dry. Lastly, put on a fair amount of oil and work the oil into the foam with your hands. You can buy special air filter oil or use regular 30w engine oil. 90w gear oil also works good. Check your shop manual. Some people say to dip the filter in the oil and then squeeze out the excess. This works, but the engine will usually run quite a bit rich for up to an hour or so, as the excess oil is pulled out of the filter, and into the engine. To avoid this, I drip a good quantity of oil all over the foam, inside, outside, and on the edges. Then, I work the oil in with my fingers and add some more till all parts of the filter are coated with oil. Sometimes, there is a coarser foam filter on the outside of the fine foam filter, clean and re-oil it the same as the fine foam filter. As you clean the foam, rub it somewhat roughly. If the foam easily rips or falls apart, get a new one. This type of filter will just fall apart with age. Ozone in the air, I guess. Anyway, if it easily rips, get a new one.