TUSA Freedom Film Anti-Fog Sheets for 2-Window Dive Mask, Clear will keep your favorite mask fog-free while diving or snorkeling. Made of a long-lasting, clear, durable urethane, the Freedom Film can be installed easily on any two window mask and is reusable with proper care. Installation is a simple, three step process. First, gently apply the film to the center of the lens. Next, while holding down the film with one index fingertip, repeatedly slide the other index fingertip from the narrow end of the film outwards, pressing out any air bubbles. When all air bubbles have been eliminated, you’re ready to dive. (Full instructions included inside package)