It is on record that a UNI foam filter has easily lasted for 5+ years of continuous use. And they can be used either oiled or dry as such, with the preference being ours in regard to filtration requirement. And most cotton gauze filters require oiling also. 5 years of life is definitely a lot in my opinion. When oiled , these foam filters move more air AND provide better filtration. A better combo would be Peter's AIR + UNI foam filter. But that's just me, and i wouldn't touch a cotton gauze filter. Rest Peter would know more. Plus, we can always use a foam filter wrap to wrap around the basic cotton gauze filter to provide better filtration. Gurjinder.