At a minimum, lenses for watersports should have good impact resistance. Glass lenses, while offering great visual clarity, are not suitable for sports. Glass is liable to crack or even shatter on impact, leading to a potential eye injury. Trivex and Polycarbonate offer the best impact protection, closely followed by polyamide (nylon).
The next consideration is optical clarity, and here we look at the ‘Abbe’ value. The higher the Abbe number, the better the optical clarity. Having discounted glass as a suitable material, the materials with the highest Abbe values with good impact resistance are polycarbonate, Trivex and polyamide.
Weight is also an important factor to consider. Heavier lenses may cause the frame to slide down your nose – which would be irritating unless you have a retention leash to hold the frame in place. Also, if you are planning to have long sessions on the water, the lighter the better for lasting comfort. Polyamide is the lightest lens material, closely followed by Trivex.
The refractive index of the lens is also something to bear in mind, and this is related to lens thickness. A lens with a higher refractive index is thinner. Polycarbonate is the winner here.
A final consideration is the scratch resistance of the lens material. While mineral glass has excellent scratch resistance, it is unsuited to impact sports. Both Polycarbonate and polyamide have average to good scratch resistance.
Note that many brands will offer an ‘anti-scratch’ or ‘hard coating’ to increase the scratch resistance, but the plain truth
is that polycarbonate, polyamide or Trivex lenses are liable to scratch if you do not look after them. ‘Scratch-resistance’ is