The air filter is a necessity for your engine. It's what prevents dust, pollen, and debris from making its way into your fuel system, and for years air filters were just a simple pleated paper element inside a frame. Then, in 1969, K&N developed a reusable cotton-element air filter that provides superior filtration with low restriction and great flow, enhancing performance and fuel economy.
Source | K&N
In the '90s, most vehicles came equipped with a cabin air filter to prevent particulates from entering the vehicle's HVAC system, and K&N stepped up to adapt its engine air filter technology for that application.
So let's talk about cost: These products are significantly more expensive than their competitors' disposable filters. Is the K&N air filter worth it?
Considering the boost in fuel economy and power from a K&N engine air filter, millions of customers believe they're worth the extra cost. Millions more report an improvement in heating and AC performance with a K&N cabin air filter, so you can draw your own conclusions. Is it worth more money for your own comfort and to avoid odors and allergens?
Bear in mind that a K&N filter will last the entire life cycle of your vehicle, rather than having to be thrown away and replaced every 12,000 miles. When you take it all into account, we say the pluses outweigh the minuses.