As many other customers have pointed out these filters are not standard sizes. Compared to Honeywell and 3M filters, they are almost 1/2 inch smaller and allow air to flow through the sides. The air resistance also seems to be very high. Produces a whistling sound that cannot be heard with any other filter. Very thin. A 20x20 filter looks like a bowl in a day. Make yourself more solid and buy a quality product. Complete garbage!
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