they have a billet casing which the filter element goes inside of. this element is reusable and washable. also unlike normal oil filters which stop filtering when pressure goes over idle, they filter continuously. they also flow better than the paper filters and catch smaller particles. they usually run about $100 for cheap ones and $200 for the really nice ones, money well spent in my mind because they greatly lengthen the life of the engine.
http://www.gopurepower.com/site/prod...lt.asp#FILTERS