Trivex lenses are a relatively new development in the lens world. Trivex lenses have a 1.53 index which makes them a bit thinner than regular plastic lenses, and a bit thicker than polycarbonate lenses. The Trivex lens material is lighter than polycarbonate, and also has better visual acuity than polycarbonate, and is also recommended as a safety material similar to polycarbonate.
However, there are few choices in Trivex lenses and Trivex is more expensive than polycarbonate lenses. While Trivex has a slightly lower refractive index than polycarbonate (making it slightly thicker), its specific gravity, makes it light and gives it better optical clarity. This means the lens may be a little thicker than polycarbonate but similar in weight. Trivex is an excellent choice for sunglasses, because Trivex accepts tint better than polycarbonate and the lenses can become darker. Trivex is also available with polarization. Similar to polycarbonate, Trivex has inherent UV protection and is an excellent choice for rimless drill mounted frames.