Polycarbonate

Polycarbonate lenses are growing in popularity because they are the thin and light in weight. They are also the most impact resistant lenses available today, and are commonly used for children's glasses, sports glasses and safety glasses.  If, however, you do not require the safety aspects of polycarbonate lenses, a high index material is a better choice.

High Index
For people needing  a strong prescription, High Index  produces a thinner, lighter, more attractive lens without compromising optical quality.  New ‘glare-free’ materials produce the clearest optics ever.

Plastic
CR-39 plastic is more widely used than glass for eyeglass lenses. It's lighter in weight than glass, but not as scratch resistant.  Usually, a scratch resistant coating is highly recommended for plastic lenses.

Glass
Glass lenses used to be the only choice for corrective lenses. Glass provides good scratch resistance and can accommodate a wide range of prescriptions. However, glass is heavy and can be uncomfortable to wear. It's also easier to break or crack.  The improvements in other materials has caused glass to be the least used material.