SECURELY RETAIN - Snugly fit and tough. can securely keep your glasses on. no more worry about the glasses slide off the nose when sweaty or looking down. Perfect for those who wear glasses while running or kids with glasses playing sports. SOFT & LIGHTWEIGHT - Ultra comfortable. very soft on the ears and nicely keep glasses on during sports or rough boy play. It is flexible enough for you to slide glasses off your eyes while reading/doing close up stuff. QUICK DRYING - Soft silicone material. quick drying and keeps you from losing the shades/glasses in a sudden burst of surf at the beach. Perfect for the water/amusement parks. beach or anywhere you're afraid you might lose the glasses. UNIVERSAL FIT - Fits most eyewear to prevent from slipping during rough boy play and securely retain on head. neck. Recommend for anybody who wants to keep glasses right on and stay put safely and gracefully. NOTE: Please note that the size does not mean the length of strap. it refers to the silicone round head. Small Round-Head: 0.11"(3mm). Large Round-Head: 0.2"(5mm). PERFECT LENGTH - It is precisely cut without any excess strap dangling down your back. short enough to securely wrap around your head and long enough to take glasses off your face and hang them around the neck when not in use.