Depth filters are the variety of filters that use a porous filtration medium to retain particles throughout the medium, rather that just on the surface of the medium. A graded density allows larger particles to be trapped near the surface while smaller particles penetrate the larger open areas to be trapped nearer the center of the filter in the smaller openings. We use depth filters because relative to other types of filters, they can retain a large mass of particles before becoming clogged. Depth filters provide the most effective filtration process and typically last longer.