The Bliz Tracker Ozon Sunglasses transition from summer trail runs to winter ski tours with ease. Bliz's Jaw Bone technology removes the frame's bottom half for summer, adds side shields for winter, and even allows you to switch out the lenses with the extra pair included with these sunglasses. These Unbreakable Polycarbonate lenses are ten times more impact resistant than standard plastic or glass lenses. Bliz made the Tracker's frame out of flexible, superlight, and surprisingly strong grilamid TR90, and there are grippy pads at the nose and temples that you can adjust for a secure fit. Proposition 65 Warning for California Consumers: This product contains chemicals known to the State of California to cause cancer andor birth defects or other reproductive harm.