Dustless 11 in. L X 13 in. W Certified HEPA Filter 1 pkThis replacement HEPA filter can be used one of two ways. Use it as a replacement on a Dustless HEPA Vacuum that was factory certified and your vacuum will retain its certification, important when working under OSHS and NIOSH guidelines. The Micro Pre filter is very economical and captures airborne particles down to 0. 5 microns, amazingly close to the 0. 3 micron level of the HEPA filter. That means the lower cost Micro Pre filter captures the