Which term describes a material's resistance to heat flow?

Which term describes a material's resistance to heat flow?

• A. Thermal resistance
• B. Thermal transmittance
• C. Heat capacity
• D. Thermal emissivity

Answer: (A)

Thermal resistance describes how hard it is for heat to flow through a material. In conduction, heat transfer per area is governed by q = ΔT / R, so a larger R means less heat moves for a given temperature difference, making the material a better insulator. For a single slab, R = L/k, with L as thickness and k as thermal conductivity; a thicker layer or a material with lower k increases R. When multiple layers are combined, their resistances add up: R_total = Σ (L_i / k_i). The reciprocal of this total resistance gives thermal transmittance (the U-value), which indicates the overall rate of heat transfer per area; lower U-value means higher resistance to heat flow. The other terms describe different concepts: thermal transmittance measures how much heat passes through, heat capacity is about the energy required to raise temperature, and emissivity concerns how efficiently a surface radiates heat.