Uninsulated garage doors typically have just one metal or wood panel and provide little more than a barricade for your garage. On the other hand, insulated garage doors are made of two panes or a thin door frame that is lined with an insulating material.
Non-insulated garage doors have a very low thermal efficiency value, which is a fundamental flaw in them. In the end, it means that some of the money you spend attempting to heat your home will just be wasted come winter.