The Atomic Aquatics SubFrame Mask is so durable, it carries a Lifetime warranty against frame breakage. The strength comes from the internal frame (subframe) molded directly beneath the surface of the silicone rubber skirt (patent pending). Subframe masks are available in Regular, Medium Fit (for narrower faces), and Slim Fit. Our Slim Fit design features a smaller, higher nose pocket and a narrower nose bridge to accommodate geometry common to most facial profiles.