The Most High Tech Membrane Technology: 1. Open windows for good air but not PM2.5 2. Leave the windows open and worry-free about dusty floor 3. It's waterproof, so you can leave the windows open on the rainy days 4. Translucent but invisible, good for privacy In Windy Condition: Smog Stoppper Still Block 95% PM2.5 For You When the filter of air-conditioning or air purifier is get dirty, which means that the air quality in the home is not clean. On the other hand, in house we breathe same air as air purifier does. That also mean “We are using our lungs to filter the air. PM2.5, smog, automotive Emission... those pollution will blow into the home with the wind, and the inhouse air quality is getting bad. You can close the window to block the pollution come into the house, however the room lacks fresh oxygen and makes it sultry and uncomfortable. :dc Smog Stopper work as the Mask for Window, It will block PM2.5 outside, and bring in fresh air into the house. When Indoor air quality is good, pollution is reduced, cleaning time is reduced, and life will be better.