For what it's worth this is from K&N's web site.... see the link below.....

"We design our air filters to provide superior filtration of the contaminants that can harm your engine while maximizing the airflow characteristics of the filter in question. The ability of an air filter to protect your engine is generally measured using a testing procedure developed by the Society of Automotive Engineers identified as the SAE J726 procedure. We subject a sample of our filter designs to this test procedure using Coarse Test Dust, which includes particles ranging in size from less than 5.5 microns to 176 microns. As a point of reference, a human hair is approximately 50 microns in diameter. The result of the above test procedure is a specific air filtration efficiency number. This efficiency number represents the percentage of test dust retained by the filter and thereby kept out of an engine. Our goal is to design our air filters to achieve maximum airflow while targeting overall filtration efficiency at 98%.

Because no two air filters are alike, the specific airflow and overall filtration efficiency will vary depending on the filter in question. However, you can rest assured that each air filter we sell, has been designed to achieve high air flow while providing superior filtration."

http://www.knfilters.com/facts.htm#FACTS

I know that K&N is in the business of selling filters and like any manufacture can slant things in their favor, so if there's something out there that can refute what they clame I'd like to see it. I'll quit using them in a flash if I can be convinced they're not doing the job.