L15 Series filter cartridges are comprised of multi-layers media. The unique construction results in a highly porous, continuously graded pore structure with a tighter inner layer and several outer prefilter layers to substantially increase the dirt holding capacity. This filter structure provides excel-lent flow rates at low pressure drop and high throughput while achieving submicron retentions, high efficiency, and extraordinary dirt holding capacity. The filter media and its support structure are thermally welded to the end caps, making integral filter cartridges of minimum extractables in a wide range of fluids and applications. All the filter cartridges are manufactured in a clean room environment.