This 20" x 30" fiberglass disposable air filter is made of progressively dense layered fiberglass media. The layers consist of looser fibers at the front that filter larger particles of dirt and lint. The layers become increasingly dense to collect finer particles like dust and pollen. These fibers are also treated with an adhesive which prevents fibers from breaking off and traveling into the airstream. The 1" depth filters are enclosed in a rigid chipboard frame with a fiberglass scrim backing for stability, allowing for for safe installation, removal and disposal. Commonly used in applications such as industrial, commercial, restaurant, school and office buildings.