Skirt and Lens Materials.
The two main components of a mask are its lenses and skirt. A quality mask skirt is typically made of a surgical grade silicone; however less expensive snorkeling mask skirts can be made of PVC (similar to the material found in plumbing pipes and offer less quality and comfort). PVC is a less durable material when exposed to sunlight or any chemicals in sunscreen while silicone skirts are softer, more flexible in following the outline of the face, and have been known to last longer and endure the elements (surgical grade silicone masks tend to create a much better seal around the face and be very comfortable to wear because of how flexible and soft they are.) A good quality mask will usually have a dual silicone skirt to seal water out while allowing the mask to move with your facial muscles more naturally.
As snorkeling is a very visual sport, quality lenses are important. A masks lens is the portion of glass within the mask frame that allows your eyes to see normally underwater. Mask lenses are not made with a traditional glass and are instead made with tempered glass, a tougher, safer type of glass. Tempered glass is more durable and up to six times more resistant to breaking than normal glass. Tempered glass also does not shatter like normal glass; the glass crumbles into large pieces instead, avoiding serious damage to the eyes. Cheaper “pool style” masks are typically made with plastic lens. These scratch and discolor easily, making for a disappointing experience. Guess which type you would like for you next tropical adventure??