• Fogging: CR-39 responds more favorably to changes in temperature than glass lenses. That is, it is less likely to �fog-up.�
• Weight: Plastic lenses are approximately 50% lighter than crown glass lenses of comparable size and shape, resulting in significantly greater comfort for the wearer.
• Reflections: Internal reflections and surface glare is less with plastic lenses than with glass.
• Tinting: Lenses may be tinted virtually any color desired. Even lenses with variable thickness such as those with high minus or plus powers will tint uniformly.
• Industrial Applications: In addition to being more impact resistant than glass, plastic lenses are actually more resistant to pitting from certain welding and grinding operations.
• Scratching: Since the surface of a plastic lens is softer than its glass counterpart, it does tend to scratch more easily. However, the many excellent scratch resistant coatings available today have generally solved this problem.

Polycarbonate:

• A high index of refraction combined with a low specific gravity make lenses made of this material especially thin and light in weight. However, its low V-value means there are significant amounts of chromatic aberration present, especially in higher powers where minimizing the thickness and weight becomes important.
• Extremely Impact Resistant: The high degree of impact resistance, make polycarbonate lenses particularly useful for industrial safety applications as well as for use in children�s eyewear.
• Scratching: Although highly impact resistant, the surfaces of polycarbonate lenses are soft and scratch very easily. An excellent scratch resistant coating must always be used with this material. Also, because of its softness, special techniques must be utilized in the fabrication of eyewear made from polycarbonate.
• Tintability: Generally, only light tints are available with polycarbonate lenses. In fact, it is the coating which absorbs the color, rather than the material itself. Lens manufacturers are continually working to improve lens coatings in an effort to increase the versatility of this material.