The key to efficiency is based on compressing the element axially and forcing it to expand radially against the tapered walls of the housing. This forces the air to pass between the tightly compressed layers along the length of the element, creating a true depth filter versus the conventional method of passing the air through layers of media. Using this unique method of filtration creates a labyrinth of sub-micronic openings from the interlocking fibers on the fabric surfaces, entrapping particles as small as .01 microns.