A K&N air filter is a replacement made of layers of cotton gauze 
between a wire mesh to hold its shape and covered (saturated) with 
an oil. It passes more air than a paper filter, and due to the oil, 
filters better than a paper element. It can give you more power
at higher RPMs and increase your MPG slightly (~1MPG).

The filter is pre-oiled and ready to install. Eventually you will need
the cleaning and re-oiling kit, which costs about US$20 and comes with
spray cans of cleaner and oil.  K&N warranties their filters for 
1 million miles when properly cared for, so the overall cost can be
dramatically lower when compared to disposable paper air filters.

Filter # 33-2030 is the same size as the stock RAV4 air filter. 
Installing this is the same as installing a Toyota filter.

K&N's home page is at <http://www.knfilters.com/>