Wool fiber diameters are around 20 micron - HEPA can have glass fibers below 1 micron, and big box retail grades are often 5 - 10 micron. Smaller fibers = bett

Wool fiber diameters are around 20 micron - HEPA can have glass fibers below 1 micron, and big box retail grades are often 5 - 10 micron. Smaller fibers = better filters.