The function of the mask is to provide a window to your underwater world, by creating air space between the diver’s eyes and the water. Clear silicone masks offer the advantages of being translucent, allowing for light penetration and creating a more open feeling. It is also softer and more comfortable than rubber.  Black silicone is the preference for some hunters and cave divers. It eliminates any light penetration from the sides and allows the diver to focus solely on what is in front of him or her, therefore, eliminating any distractions. Low volume masks are easier to clear. You have less distortion because your eyes are closer to the lenses. However, you may not have as much peripheral vision. Some masks have side windows, which give the diver better peripheral vision.  Purge masks have a one way valve that allows clearing the mask of water by simply exhaling.