CLEAN FLOW FILTRATION SYSTEM & TEK VALVES The Pro Series Bandana Dust Mask protects your mouth and your nose from harmful dust as you head down the trail. The sewn in interior filter blocks 99.5% of all dust particulates. This ensures dust-free air inhalation and a more enjoyable riding experience. The Rider Dust Mask also has (2) one-way exhaust valves which reduce lens fogging & release heat, CO², and water vapor.