3M Stacked Lens Cover FF-400-18 makes it easy to help protect the lens of the 3M Ultimate FX Full Reusable Respirators Facepiece, models FF-401, FF-402 and FF-403, while maintaining worker productivity in certain work environments. The lens cover features 7 layers that can be easily removed as they become contaminated. As a layer is removed, it reveals a fresh, clean layer underneath.