K&N Engineering has been manufacturing air filters for over 30 years. The company uses an oil-impregnated, cotton-gauze filter element surrounded by a wire mesh. This design is superior to a paper element because it allows for superior airflow while maintaining effective air filtration. The cotton material lets air pass through it easily while trapping particles in the sticky, oil-covered fibers. This system works for up to 50,000 miles, at which point the filter is cleaned, re-oiled, and ready for another 50,000 miles. These filters, by the way, are emissions legal in all 50 states and do not void the manufacturer's warranty.