Pepper's Speedline Metals Polarized style is designed with a Monel Metal frame that is lightweight and strong. Monel metal is a high quality optical material developed in the aircraft industry. Spring hinges offer additional durability and comfort. Megol nose pads secure fit and resistant to slippage from lotions and sunscreen. Tri-acetate polarized lens features 2 acetate lens with a polyvinyl acetate layer sandwiched in between.