Paper & Foam vs K&N  

By comparison, paper filters are made from compressed fibers. The spaces between these fibers provide microscopic holes the air must pass through. One by one, these holes become plugged with dirt and dust particles. Once a hole becomes plugged, the air must find an alternate route through the medium. As the filter collects more dirt, its resistance to air flow increases because there are fewer and fewer holes left open and as restriction goes up, horsepower and fuel economy go down. But to meet minimum filtration standards, the paper must be thick and/or the fibers must be tightly compressed and dense. Therefore paper elements that provide adequate filtration are restrictive to air flow by design. Any paper element that could flow as much air as an equivalent K&N would not provide safe filtration.

Disposable Paper Air Filter
	Pleated wood pulp bonded together. As dirt builds, passages are plugged and filter must be replaced in approximately 10,000 miles. Irregular passages filter out dirt on a go/no go basis. As fibers swell from moisture or oil blow-by vacuum pressure increases and airflow decreases. Turbulent filtered air.

In recent years the foam construction filter has been touted as possibly a better alternative to the conventional paper type.

Follow the explainations below, and you will see why the concept has its own set of problems, and although some have been advertised as cleanable and
re-oilable, we have to ask, have you ever tried to clean one?

APT has tested many filters, it always seems to us that foam elements fall into two groups:
1./ Those that filter adequately, but strangle your engines power potential, and ...
2./ The other group lets in the air, unfortunately, the dirt very often finds its way through also! The dirt remaining in the middle of the element, in our experience
at least, cannot be washed out.

Typical Foam Air Filter
	Open cell foam usually saturated with oil. Dirt builds on outside and blocks the openings. Higher vacuum pressures distort the cells drawing dirt deeper into the filter. Airflow is reduced as cells become blocked. Turbulent filtered air.

The K&N air filter is somewhat more complex. The unique design features an oiled cotton fabric which holds airborne dirt particles. These dirt particles cling to the outside of the filter and actually become part of the filtering media. The cotton fabric is sandwiched between pleated aluminum screen. Pleating increases surface area which in turn promotes air flow and prolongs service intervals. Pleating exposes five times the surface area compared to a flat element like foam.

The dirt particles collected on the surface of a K&N element have very little effect on air flow because there are no small holes to clog. Particles are stopped by crisscrossed cotton fibers and held in suspension by the oil. As the filter begins to collect debris, an additional form of filter action begins to take place because air must first pass through the dirt particles trapped on the surface. That means the filtration efficiency of a K&N element actually increase as the filter collects dirt. Tests have shown a K&N E-1500 (most common domestic V8 element) filter will flow 60 percent of its maximum flow capacity after 50,000 miles of street use. And, considering a new K&N flows half again as much air as a comparable paper element, that same filter will provide all of the air the engine needs even after 50,000 miles.

Conversely, dirt trapped by a paper element will impregnate the fibers which will impede air flow at a proportional rate. In other words, performance decreases dramatically as a paper element gets dirty. At the service interval, say 14,000 miles, air flow through a paper element can decrease as much as 70 percent. The efficiency of K&N's oiled cotton gauze medium has been proven time and time again.
Some heavy trucks have logged over 100,000 miles with no loss in air flow as reported by the service technicians. Again this is due in part because a clean K&N filter will flow half again as much air as a comparable paper element.

A K&N will provide superior filtration without sacrificing air flow for a longer period of time - that's performance with value.