These MERV-17 rated filters capture the finest dust! They have 3 layers: The first layer is 1 micron, the 2nd layer is the HEPA layer and captures 99.98% of 0.3-micron particles, and the 3rd layer is a fiberglass-reinforced layer to strengthen the HEPA layer. Fits any dust collector with a 14-1/2” diameter top.