Thermal Conductivity Compared

Thermal conductivity k measures how well a material conducts heat. Units: W/m·K.

k_metals: Cu ≈ 400, Ag ≈ 430, Al ≈ 240, Fe ≈ 80, Steel ≈ 50.

k_insulators: glass ≈ 0.8, wood ≈ 0.15, concrete ≈ 1, brick ≈ 0.7.

k_fluids: water ≈ 0.6, air ≈ 0.025.

k_air is very small — that's why fluff insulation works (trapped air pockets).

Wiedemann-Franz law: for metals, k/σ = (π²/3)(k_B/e)²·T — linear relation to electrical conductivity.

Materials with low k are used as insulators (foam, fiberglass, wood, plastic).

Materials with high k are used in heat sinks (copper, aluminum).