What does U-value measure?

U-value measures thermal transmittance through a material, which quantifies the rate of heat transfer through building components such as walls, windows, and roofs. It indicates how well a building element insulates against heat flow; a lower U-value signifies better insulating properties, meaning less heat is lost or gained through that material. Understanding U-value is critical in the design and evaluation of energy-efficient buildings, as it helps architects and engineers select appropriate materials to enhance energy conservation and comfort.

In contrast, the other options refer to different domains: electrical resistance relates to how easily current flows through a circuit, while mechanical strength pertains to how materials withstand forces without deforming or breaking. Fluid dynamics deals with the behavior of fluids in motion and their interactions within pipelines. Each of these concepts plays a vital role in their respective fields, but they do not pertain to the thermal characteristics measured by the U-value.