Your oil filter is probably one of those things you just blindly replace every time you take your motorcycle to the mechanic to have preventative maintenance service done, or if you're the hands-on type and do it yourself. It's easy to not really give a damn about the inner workings of an oil filter, and simply trust what the manufacturer says.
I, for one, have been working on my own bikes for years, and only very seldom have I bothered to check what the filter was actually made of. That said, we're often led to believe that the most expensive option is always the best. Our talented colleagues over at FortNine released an extremely detailed video showing how the technology in each type of filter works, as well as determining which one is best. Each filter type was put through a series of rigorous tests, and the results may surprise you.
Paper filters are what you'll most commonly find on your OEM oil filters. They're cheap, easy to produce, and in FortNine's testing, the overall best. For starters, thanks to its fibrous structure made out of a combination of cellulose, cotton, wood fibers, and other stuff that's really absorbent. This means it can pull water out of your oil to prevent rusting. The paper filter displayed an adequate flow rate at 24 PSI, while having the best overall capacity.
As you probably know, an oil filter's job is to filter out gunk, metal shavings, and particulate, while ensuring oil actually still gets to your engine. The good old paper filter was able to withstand the most metal shavings before clogging—34 teaspoons of aluminum shavings. Last but not least, efficacy. The paper filter was the best and was able to clean the used engine oil to a ferrous metal index (FMI) of 16, from an originally much higher 21; and 16 parts per million (PPM) of contaminants, from an initial reading of 20.
In Fortnine's rigorous testing, the steel filter had the best flow at 22 PSI with the same pump power. In theory, this means less stress on the engine due to increased oil flow. Steel filters are also extremely robust, and can withstand immense heat and pressure before failing. However, in FortNine's test, the steel filter was the first to clog, with just 9 teaspoons of particulate before failing completely. Lastly, the steel filter was hardly able to clean the used motor oil, dropping the FMI to 19, but letting slip all 20 parts per million of particulate.
Fiberglass filters are often marketed as the best of both worlds—the efficacy of a paper filter, with the robustness and slick flow-rate of a steel filter. They're also the most expensive. However, FortNine's test proves that fiberglass filters aren't all that great. For starters, the fiberglass filter had the most restrictive oil flow at 25 PSI. Secondly, although it didn't clog as quickly as the steel filter, it still clogged much sooner than the paper filter, at just 14 teaspoons of particulate. Lastly, the fiberglass filter wasn't that efficacious, either, dropping the FMI to 20, and the PPM to 18.