Which value represents the resistance which is the reciprocal of conductivity?

• A. R value
• B. U value
• C. Thermal inertia
• D. K factor

Answer: (A)

Heat moving through a material is governed by its conductivity: higher conductivity means easier heat flow, lower resistance. The measure that captures how much a material resists heat flow is the thermal resistance, which for a layer is defined as R = thickness divided by conductivity (R = L/k). That means the reciprocal of conductivity, 1/k, relates to resistance per unit thickness, and combining layers adds their resistances. In practice, this resistance is expressed as the R-value, the standard way to quantify how well a material or assembly resists heat flow. The other terms don’t represent this resistance: U-value is the overall heat transfer rate (the inverse of total R), thermal inertia concerns heat storage, and K factor typically denotes conductivity in some contexts rather than resistance. So the value that represents the resistance, i.e., the reciprocal of conductivity, is the R-value.