What is R-value vs U-factor for garage doors?
U-factor measures the total heat transfer rate of an entire garage door assembly, while R-value measures insulation resistance of the material alone; U-factor is the more accurate metric for comparing real-world thermal performance.
When shopping for an insulated garage door, you will see both R-value and U-factor listed on specifications. These numbers describe insulation performance but in different ways. R-value measures the insulating power of the door material itself, expressed as resistance to heat flow per unit of thickness. U-factor, by contrast, rates the entire door assembly as it will perform in your home, accounting for the frame, seals, and all components together.
U-factor is the more practical number for Ontario builders and homeowners because it reflects what actually happens when heated or cooled air meets the installed door. A garage door with a high R-value material can still have poor overall thermal performance if the frame conducts heat or seals leak air. U-factor captures those real-world losses.
To read the spec: U-factor appears as a decimal between 0 and 1, usually written as "U-0.15" or similar. The lower the U-factor, the better the insulation. R-value is shown as a whole number like "R-12" or "R-18." When comparing doors, use U-factor as your primary guide, since it tells you what the complete door will actually deliver. Builders and manufacturers in Ontario typically provide both numbers on their product sheets, but focusing on U-factor gives you a more honest picture of performance across different door styles and construction methods.