100 Dust Masks For Airborne Substances. This is a new set of 100 dust masks. These masks are disposable, light weight, comfortable and have good filtering efficiency making it easy to breathe. Each box contains 50 masks. They filter out fiberglass dust, saw dust, household or garden dusts and fibrous producing dusts. Each mask measures approximately 4 3/4" (120 mm). We work hard to update our descriptions and pictures of our merchandise. As part of a process of ongoing innovation by our suppliers, newer versions of the item shown may be shipped before we are able to complete an update. As a result there may be a slight variation in color and design.