The K&N Air filter panel brings in cleaner air going into your engine. And you do not have to throw it away at every car service, so it saves you money in the long run. All you need is the K&N cleaning kit, which you can use to clean the filter panel and it'll be as good as new!
I am using K&N Air filter panel model KN-33-2819 for this Ford Focus car. I got it cheaply via ebay - click here to search for 33-2819
This is a quick guide to show you how to do this job very easily without any fuss. Click for bigger picture.