Many cartridges claim to be depth filters. But to be a true depth filter, a cartridge must be able to retain contaminants throughout the entire cross section of the filter. 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. Without graded density, a so-called "depth" filter will operate in practice only as a surface filter. The Purtrex filter has the graded density that is required to be a real depth filter. The Purtrex depth filter is an exceptional value for general applications where long life, high purity and low change-out frequency are required. Produced through GE Osmonics patented melt blown micro fiber technology, Purtrex is a 100% pure polypropylene depth filter with exceptional dirt-holding capacity. Purtrex true-graded density filter matrix (lower density at the surface of the filter with progressively higher density toward the center) captures particles throughout the entire filter depth. This translates to longer life and fewer change-outs than existing string-wound or resin-bonded filters. Purtrex contains no wetting agents, solvents, anti static agents or binders, and meets the requirements of the FDA for food and beverage contact. The filter incinerates to trace ash for easy disposal.