Strong, spring supported plastic.
Very sturdy pair of reading glasses. They feel pretty good wearing for periods of time, but could be slightly larger for my face. For extended periods of wearing I start to notice a little tightness. It's hard to tell when ordering glasses online if they're going to fit perfectly. Arrived in pristine condition and with a smooth, soft case for protection. Would receive five stars if they were just slightly larger.
Rating: 4 stars