A disposable mask fits over the nose and mouth. It removes very small particles from the air you breathe. These particles include germs (like viruses, bacteria, and mold) and other kinds of dust. A disposable mask does not have replacement parts. Surgical face masks are made with non-woven fabric, which has better bacteria filtration and air permeability while remaining less slippery than woven cloth. The material most commonly used to make them is polypropylene, either 20 or 25 grams per square meter (gsm) in density.