If vision quality is the priority then choose glass lenses. Choose a plastic lens if safety or impact-resistance is required.
Quality glass lenses offer the best viewing quality and the most scratch-resistant. They will be heavier, cost more money and are more prone to shatter when hit.
Organic plastic (CR-39)
CR-39 organic plastic is thinner and weighs half as much as glass. It exceeds the FDA requirements for impact-resistance.
A remarkable strong plastic, it weighs the least and is the most impact-resistant making it a perfect choice for rugged sunglasses. They also offer built-in ultraviolet. These are a good choice for kids sunglasses, sports and outdoor activities, and safety glasses.