WHAT DOES IT MEAN?
A U-value describes the rate of heat transfer through a building element for a given area and temperature difference; a lower figure indicates less heat transfer under the stated conditions.
In practice
For a garage door comparison, check whether the figure describes an individual panel or slat, or a complete door. These are not interchangeable. Door size, joints, perimeter details and the stated test or calculation method matter.
An insulated curtain is only one part of the garage. Walls, roof, ventilation, floor and gaps influence how the space feels. Do not infer a particular energy saving or indoor temperature from a material description or a panel value alone; ask for comparable whole-door information where available.
