This Metal Mesh Pre-Filter is made of standard bonded aluminum metal mesh filter media in a heavy duty aluminum frame channel. Good Filter Company also adds 1 layer of expanded aluminum on the out flow side of the “SD” models and a layer of expanded aluminum on both sides of the “HD” models.This is a better quality bonded aluminum mesh pre-filter than the one that is standard with nearly all residential and commercial electronic air cleaners. It is a washable, permanent, bonded aluminum metal mesh pre-filter. The frame channel is mechanically closed so it grips the filter media more securely and mechanical closing also flattens any sharp edges on the corners. Our standard duty aluminum frame channel is heavier duty than the frame channel used by other manufacturers, and has rounded edges so it won’t split like most of the lighter duty sharp edged filter frame channels. The frame channel is secured on one corner by an aluminum rivet, not a thin metal tab that can break like other aluminum mesh pre-filters. Although it is commonly called a 3/8″ thick bonded aluminum metal mesh filter, the actual thickness is 5/16″. It can also be squeezed to 1/4″ for applications requiring thinner filters. No one else makes pre-filters like this. This is a superb quality metal mesh pre-filter and will function well for long periods with normal cleaning maintenance.