Due to the way that safety glasses or goggles should fit, close to the head keeping dirt and debris out, it can cause moisture build up, especially if the wearer is doing a physical job which can result in the lens fogging. How you choose which coating you need depends on the environment and the application being performed. Some coatings offer anti-fog performance on the inside, where it is most needed, and a scratch-resistant hard coat on the exterior of the lens. Others are anti-fog and scratch resistant on both sides making them suitable for environments with high humidity.
However, not all anti-fog coatings are created equal. The tests conducted for the coating performance are optional tests for manufacturers, requiring the anti-fog coating to perform for a minimum of 8 seconds on first use. Where many coatings fail is in the longevity of the anti-fog performance.
Traditional hydrophobic anti-fog coatings are soap-based, washing off after a handful of cleans, making the eyewear ineffective and unusable. As soon as lens coating performance diminishes, employees try to compensate and compliance drops rendering the eyewear useless. Therefore, it is important to look out for manufacturers of permanent hydrophilic coatings that have been bonded onto the lens and last the life of the eyewear.