Our sunglass collections frames are generally made from plastic, nylon, a metal or metal alloy. Nylon frames are usually used in sports because they are light weight and flexible. They are able to bend slightly instead of breaking when pressure is applied to them. This flex can also help the glasses grip better on the wearer’s face. Metal sunglass frames are usually more rigid than nylon frames thus they can be more easily damaged when participating in sporty activities, but this is not to say that they cannot be used for such activities. Because metal frames are more rigid, some models have spring loaded hinges to help them grip the wearer’s face better. The end of the ear pieces and the bridge over the nose can be textured or have a rubber or plastic material to hold better. The end of the ear pieces are usually curved so that they wrap around the ear; however, some models have straight ear pieces. Oakley, for example, has straight ear pieces on all their glasses.