Pollution Safe anti pollution dust mask is made up of 4 layers that will help to filter out 95 percent of the pollutants in the environment helping you breathe clean air. This mask is suitable for all ages. It comes in one size that fits all ages with the elastic ear loops. Function of the valve: When you breathe in, the respiratory valve will close to prevent polluted air. When you breathe out, the respiratory valve opens up to expel the air from your lungs. Dust masks with a valve help in easier breathing and reduce the build-up of heat and humidity.