Heavy-Duty, Permanent, and Washable Aluminum Filter Captures large dust particles, useful upstream in your air intake to protect your HEPA or pleated filters downstream Heavy duty Aluminum Frame, with expanded and bonded aluminum filter media, the rear of the filter features a layer of expanded and corrugated Aluminum to support the filter in High-CFM applications. See-through by design- meant for high flow and not for small particles. Heavy-Duty, Permanent, and Washable Aluminum Filter. Captures large dust particles, useful upstream in your air intake to protect your HEPA or pleated filters downstream. Heavy duty Aluminum Frame, with expanded and bonded aluminum filter media, the rear of the filter features a layer of expanded and corrugated Aluminum to support the filter in High-CFM applications. See-through by design- meant for high flow and not for small particles. MERV4 rated.