Pad Refills (Pack of 6 Pads) - 18 1/2" x 18 1/2" x 1" Quantity:Default The permanent frame is constructed

The permanent frame is constructed of space-age plastics that are resistant to corrosion

some just refer to them as electrostatic filters

The "Practical Pleat" contains over 500% greater surface area than a MERV 10 one-inch pleat

Either way

28X Increased Efficiency

Pad Refills (Pack of 6 Pads) - 18 1/2" x 18 1/2" x 1" Quantity:Default The permanent frame is constructedPACK of 6 pads for Pad and Frame Air Filters Filtering inserts are anti microbial and are more efficient in capturing particles, such as dust, ragweed, pollen, etc., from the air stream, than standard fiberglass filters purchased at retail outlets. Filtering inserts are shipped in an easily stored packet.