Glasfloss Industries SGP20256M132PK Z-Line Series 700 SG MERV 13 Air Cleaner Replacement Filter Option, 2-Case Replacement option for Aprilaire Space-Gard #201and #401 Media MERV 13 Performance Convenient One Piece Cartridge That Saves Installation Time Made in the USA Pre-Applied Gasket Helps Prevent Air By-pass. (Aprilaire is a registered trademark of Research Products Corporation)