Stay protected while breathing freely with the O2 Nano Mask Reusable Nanofiltration Mask. Effectively blocking 99% of PM2.5 particles, this protective face mask features innovative nanotechnology. Tucked inside the two-layer mask skin is a three-layer nanofiltration membrane. Each membrane serves its own purpose to stop everything from smoke to bacteria to some viruses. Even with all this protection, the O2 Nano Mask remains breathable, allowing more air to pass through than other masks. Designed in the USA, the O2 Nano..