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 so widely
Conductivity depends on the dominant heat-carrying mechanism in each material:
Metals rely on free electrons. Those electrons also carry electrical current, which is why good electrical conductors are almost always good thermal conductors — silver, copper, and aluminium lead the table. Alloying disrupts the electron’s mean free path, scattering carriers and slashing conductivity: stainless steel (roughly 16 W/m·K) conducts far less than pure iron (roughly 80 W/m·K), even though iron dominates the alloy.
Polymers and insulators lack free electrons, so heat travels only through lattice vibrations (phonons), which are far less efficient. Most plastics fall between 0.1 and 0.5 W/m·K.
Trapped-air insulators (foams, aerogel) achieve their very low k by replacing most of the solid with pockets of still gas. Stagnant air itself conducts poorly at around 0.026 W/m·K, and eliminating convection through tiny pores pushes the bulk value even lower.
Building materials span a wide range: a lightweight aerated concrete block sits near 0.12 W/m·K while dense concrete sits near 1.7 W/m·K — a 14× difference for materials that look similar on a building site.
Illustrative calculation
A wall section consists of 100 mm of dense brick (k ≈ 0.7 W/m·K), 50 mm of mineral wool insulation (k ≈ 0.04 W/m·K), and 12 mm of plasterboard (k ≈ 0.25 W/m·K). For a 1 m² panel with a 20°C temperature difference:
- Brick layer: Q = 0.7 × 1 × 20 / 0.10 = 140 W
- Insulation layer: Q = 0.04 × 1 × 20 / 0.05 = 16 W
- Plasterboard: Q = 0.25 × 1 × 20 / 0.012 ≈ 417 W
These would not simply be added in a real wall (layers are in series, so thermal resistances add, not flows). The example illustrates why the thin insulation layer dominates the wall’s heat performance despite its small thickness — its very low k gives it the largest thermal resistance.
How to read the table
Use the search box to jump straight to a material by name, or filter by group to compare within a category. The k column is what you need for Fourier’s law; remember these are representative values at roughly 25°C. For precision engineering — especially at elevated temperatures, with moisture, or with low-density materials where density matters — consult manufacturer datasheets.
A quick comparison across groups shows the span: aerogel at the bottom (≈0.015), good insulators at 0.02–0.05, most building materials at 0.1–2, and metals from 10 (stainless steel) up past 400 (copper). That roughly four-orders-of-magnitude spread is why material choice is the dominant variable in any heat-management design.