FMA Sweat Prevent Mist Fan Mask includes a detachable Fan System to defog the Lens. The Fan itself is the same colour as the mask and can be detached and reattached to the other side depending on whether you're left handed or right handed while resting against a cheek rest.
To work the Fan System, you'll need to twist and lift the fan lid and insert 2 AA batteries.
How it works is the Fan allows air to flow through the rubber tubing in the mask making it's way to the two gaps underneath the lens, keeping the lens fog free! It comes in BLACK, OD and DE!