Glass generally insulates better than plexiglass. While plexiglass is lighter and more durable, its ability to insulate is lower compared to glass. To match the insulating properties of glass, plexiglass sheets would need to be much thicker.
Therefore, in comparison, a standard sheet of glass provides better thermal insulation than plexiglass. However, for applications where weight, impact resistance, or clarity are more important than the ability to insulate, plexiglass remains a popular choice.