U-Factor

The U-factor, also known as thermal transmittance, measures how well a material or assembly allows heat to pass through it. Unlike insulation’s R-value, which measures resistance to heat flow, the U-factor represents how much heat is transferred. Lower U-factor values indicate better insulating performance, meaning less heat escapes or enters through the material. It is commonly used to evaluate windows, doors, and other building components in terms of energy efficiency.