Thermal Conductivity of Materials

Thermal conductivity, density, specific heat and diffusivity of 20 materials from copper to foam.

Thermal conductivity (k) says how fast a material carries heat: copper conducts a thousand times better than a plastic and ten thousand times better than foam insulation. This table lists 20 materials with their conductivity, density and specific heat near room temperature, and the thermal diffusivity (k ÷ ρ c), which says how quickly the temperature in a body evens out.

The table

20 rows

Material	Thermal conductivity k (W/m K)	Density (kg/m3)	Specific heat (J/kg K)	Thermal diffusivity (mm2/s)	Conductivity (BTU/h ft F)
Copper	401	8960	385	116.245	231.693
Aluminum, pure	237	2700	903	97.207	136.936
Brass	109	8530	380	33.627	62.979
Carbon steel (0.5 percent C)	54	7833	465	14.826	31.201
Cast iron	52	7272	420	17.026	30.045
Titanium	21.9	4506	522	9.311	12.654
Stainless steel 304	14.9	7900	477	3.954	8.609
Concrete	1.4	2300	880	0.692	0.809
Window glass	0.96	2500	840	0.457	0.555
Brick	0.72	1920	835	0.449	0.416
Water	0.598	998	4182	0.143	0.346
Wood, pine	0.12	510	1380	0.171	0.069
ABS plastic	0.17	1040	1400	0.117	0.098
Nylon 6/6	0.25	1140	1700	0.129	0.144
PTFE	0.25	2200	1050	0.108	0.144
Rubber, natural	0.13	1100	2010	0.059	0.075
Fiberglass insulation	0.043	12	835	4.291	0.025
Polystyrene foam (EPS)	0.035	20	1210	1.446	0.02
Polyurethane foam	0.025	30	1400	0.595	0.014
Air (still)	0.026	1.2	1005	21.559	0.015

Source and notes: Typical values near room temperature (Cengel and Ghajar, Heat and Mass Transfer, Appendix; ASHRAE Handbook, Fundamentals; supplier data). Alloys and plastics vary with composition, and insulation and wood vary with density and moisture. Thermal diffusivity = k / (density x specific heat); 1 W/m K = 0.577789 BTU/h ft F.

How to use this table

Find the material.
For steady heat flow through a flat layer use Q = k A ΔT ÷ L; for a layered wall add the thermal resistances L ÷ k.
Use density and specific heat for the energy stored in a part, and diffusivity for how fast it heats up.

Worked example: heat through 100 mm of wall with a 20 K temperature difference

Concrete (k = 1.4 W/m·K): Q = k A ΔT ÷ L = 1.4 × 1 × 20 ÷ 0.1 = 280 W per m².
Polystyrene foam (k = 0.035): Q = 7.0 W per m², which is 40 times less.
The thickness of concrete that insulates as well as 100 mm of foam is 4.0 m.

Notes and cautions

Conductivity varies with temperature, and with composition for alloys, plastics and wood. Insulation values depend strongly on density and moisture: wet insulation conducts much more.
Air is a poor conductor; insulation works by trapping still air in small cells.
Contact resistance at joints between solids can matter more than the conductivity of the material, especially for heat sinks.

FAQ

Which metal conducts heat best?

Silver (about 429 W/m·K), then copper (401) and gold; aluminum is 237. Stainless steel is poor at about 15.

What is thermal diffusivity?

The conductivity divided by the density and specific heat. A high value means a material changes temperature quickly when heated.

Sources

Cengel and Ghajar, Heat and Mass Transfer, Appendix Tables A-3 and A-6; ASHRAE Handbook, Fundamentals, chapter on thermal and water vapor transmission data.
Typical values near room temperature (Cengel and Ghajar, Heat and Mass Transfer, Appendix; ASHRAE Handbook, Fundamentals; supplier data). Alloys and plastics vary with composition, and insulation and wood vary with density and moisture. Thermal diffusivity = k / (density x specific heat); 1 W/m K = 0.577789 BTU/h ft F.