U-factor

U-factor is a measurement that shows how well a window, door, or building component insulates by indicating how much heat passes through it. It is expressed in units of heat transfer per square foot per hour per degree Fahrenheit (BTU/(hr·ft²·°F)). A lower U-factor means better insulation — the material allows less heat to escape in winter or enter in summer, helping to keep indoor temperatures stable and reduce energy costs. It’s a key factor in assessing the energy efficiency of building components and selecting products that improve comfort and sustainability.