The efficiency of the Pre-Filter is directly related to the life of the HEPA in that the more particulates captured in it, the less can pass through and prematurely block the HEPA. Most Pre-Filters have an efficiency grading of F5 - F7. When plastics are being lasered, the particulate size generated is typically 0.2 microns. At this level of filtration the media has an efficiency of 25% in F5 to 65% in F7. When metals are being lasered the particulate size being generated is typically below 1 micron. This equates to an efficiency of 65 in F5 to 80% in F7. The BOFA range of fume purification systems have an F8 grade media which gives an efficiency of 80% at 0.2 microns and 95% at 1 micron