This is the last dust mask you will ever need to buy. This mask will last indefinitely when properly cared for. It uses a surgical grade material to filter dust, pollen and other particles form the air that you breathe. Other benefits include: Will not fog glasses guaranteed). More cost effective than paper masks because it is reuseable. Lightweight and comfortable. Forms to all face shapes, including beards. Easy to talk and breathe through. Adjustable nose piece forms a seal to keep dust out. Three sizes are available. Medium fits neck sizes smaller than 15 1/2. Large fits neck sizes 16-19. Extra Large fits neck sizes 19-24.