In my opinion, metal glasses would be more eco-friendly than plastic glasses. Even though both plastic and metal are mined, metal is a kind of material that can be recyled and reused. However, plastic cannot be recycled. So to the environmental protection, metal glasses are better than plastic glasses.
As we know, plastic is a common material that would do greatly damage to our environment and cause environmental pollution. While Metal is more biodegradable than plastic. So metal glasses are more eco-friendly than plastic glasses.