The Aerostar® Series 400 pleated air filter is one of our most popular products. Why? Because it simply performs. The Aerostar Series 400 filter is effective at removing many airborne irritants such as pollens, molds, dander, and dust and is a great pre-filter in any HVAC application. The low resistance improves air flow and can greatly reduce energy costs. Available in nominal depths of 1″, 2″, and 4″.