Fits up to 20 x 30. Cut-to-fit. Trust: We provide the best for you. We provide Filtration for: nuclear contamination; space programs; pharmaceutical laboratories. NaturalAire cut-to-fit made with natural fibers. Holds 2x the dust compared to polyester filters. Washable, reusable and biodegradable. Low airflow resistance saves on energy cost. Excellent for systems requiring high velocity filters. Effective protection against these common household contaminants. Dust/lint. Dust mite debris. Pollen. Mold. Flanders: Foremost in air filtration. Last up to one full year. www.flanderscorp.com.