Thermal conductivity tells you how fast a material moves heat. This reference lists representative k values, in watts per metre-kelvin, for more than fifty metals, polymers, building materials, and insulators near room temperature, with search and grouping so you can find a figure in seconds.
How it works
Thermal conductivity, written k or λ, is defined by Fourier’s law of
conduction. For a flat slab the heat flow is Q = k · A · ΔT / d, where A is
the cross-sectional area, ΔT the temperature difference across the slab, and
d its thickness. A material with a high k (copper at 401 W/m·K) passes heat
readily, while a low-k material (aerogel at about 0.015 W/m·K) resists it. The
units, W/(m·K), follow directly: watts of heat per metre of thickness per kelvin
of temperature difference.
Why the values vary
Conductivity depends on the heat-carrying mechanism. In metals, free electrons carry most of the heat, so good electrical conductors are also good thermal conductors — silver and copper top the table. Alloying scatters those electrons, which is why stainless steel conducts far worse than pure iron. In insulators and gases, heat travels by lattice vibrations or molecular collisions instead, both far less efficient, giving k values hundreds of times smaller.
Example and notes
A 2 mm aluminium plate (k = 237) with a 50°C difference across 0.1 m² passes
237 × 0.1 × 50 / 0.002 ≈ 593 kW of heat — effectively no insulation. Swap in
20 mm of polyurethane foam (k = 0.025) and the same conditions pass only about
0.025 × 0.1 × 50 / 0.020 = 6.25 W. Values here are baseline figures near 25°C;
real conductivity shifts with temperature, purity, density, and moisture, so use
manufacturer datasheets for precise design work.