Melting point and heatML-02
Thermal conductivity chart: metals, alloys, building materials, insulation, liquids and gases, and how to read W/(m·K)
A quick-reference table and seven detailed tables of thermal conductivity, each value with its temperature and source, and ranges kept for alloys and building materials.
At a glance
This article walks through 13 topics, in this order.
- In short: what is the thermal conductivity of common substances?
- What is thermal conductivity, in simple terms?
- What is the thermal conductivity of metals?
- Why do alloys have a range of thermal conductivity?
- Does thermal conductivity change with temperature?
- What is the thermal conductivity of building materials?
…and 7 more in the contents below.
In this article (13 sections)
- In short: what is the thermal conductivity of common substances?
What is thermal conductivity, in simple terms?3
What is the thermal conductivity of metals?2
Why do alloys have a range of thermal conductivity?4
- Does thermal conductivity change with temperature?
- What is the thermal conductivity of building materials?
What is the thermal conductivity of insulation?1
What is the thermal conductivity of liquids and gases?2
- What is the thermal conductivity of ceramics and plastics?
- How does thermal conductivity differ from the heat transfer coefficient?
- What happens when thermal conductivity is high or low?
Frequently asked questions about thermal conductivity6
- Jump to this section
- Which substance has the highest thermal conductivity?
- Does stainless steel conduct heat better than iron?
- How many times better does aluminium conduct heat than iron?
- What is the symbol for thermal conductivity?
- How does thermal conductivity differ from specific heat?
- How does glass compare with stainless steel?
- Sources
Thermal conductivity tells you how easily heat travels through a material.
It is given in W/(m·K), and a larger number means heat flows more easily. Metals have large values; air and insulation have very small ones.
The key point: thermal conductivity changes with temperature and composition, so always read a value together with "at what temperature, for which material".
In this article:
- A quick-reference table of common substances, and a log-scale ruler
- How to read the unit W/(m·K), and how to convert older units
- Pure metals and alloys (stainless steel, aluminium, copper, titanium)
- Building materials, insulation, liquids, gases and ceramics
- How values change with temperature
- How thermal conductivity differs from the heat transfer coefficient and the U-value
The values were checked against AIST (Japan's National Institute of Advanced Industrial Science and Technology) and NIST (the US National Institute of Standards and Technology). Manufacturers' technical data and a Japanese building-energy foundation's tables were also used.
In short: what is the thermal conductivity of common substances?
Silver and copper are in the hundreds, stainless steel is in the teens, water is about 0.6 and air about 0.026 W/(m·K).
| Substance | Thermal cond. (W/(m·K)) | Temp. |
|---|---|---|
| Silver | 429 | Room temp. (about 25 °C) |
| Copper | 386–402 | Room temp. (about 25 °C) |
| Aluminium (pure) | 226–237 | Room temp. (about 25 °C) |
| Iron (pure) | 72–80.4 | Room temp. (about 25 °C) |
| Carbon steel | 41 | Room temp. |
| Titanium (pure) | 21.9 | Room temp. (about 25 °C) |
| Stainless steel (304) | 16.3 | Not stated |
| Concrete | 1.6 | Not stated |
| Glass | 1.0 | Not stated |
| Water | 0.598 | 20 °C |
| Wood | 0.12 | Not stated |
| Glass wool (16 kg/m³) | 0.045 | Not stated |
| Air | 0.0264 | 27 °C |
Source (6)
- AIST (National Institute of Advanced Industrial Science and Technology, Japan), "Thermal conductivity of metals", Distributed Thermophysical Property Database
- Kyocera, "Fine ceramics and heat 3: thermal conductivity" (measured to JIS R 1611)
- Nippon Steel, "Stainless Steel Cold Rolled Sheets" catalog (S008, Aug. 2025)
- IBECs, "Thermal constants of materials" (from SHASE, "HASPEE", 2012)
- NIST Chemistry WebBook, "Thermophysical Properties of Fluid Systems" (isobaric data at 0.101325 MPa)
- E. W. Lemmon and R. T. Jacobsen (2004), "Viscosity and Thermal Conductivity Equations for Nitrogen, Oxygen, Argon, and Air", Int. J. Thermophys. 25 (NIST)
The table runs from highest to lowest. Each row is taken from one of the seven tables further down.
Silver, at the top, conducts about 16,000 times better than air, at the bottom. Because the gap is so large, the figure uses a logarithmic axis.
Even among metals, copper conducts more than 20 times better than stainless steel. "Metals conduct heat" is too rough a rule.
Check the temperature column too. The same material gives a slightly different value at a different temperature.
What is thermal conductivity, in simple terms?
Thermal conductivity is the heat that flows each second through 1 m² of a plate 1 m thick when its two faces differ by 1 °C.
The usual symbol is λ (lambda). Many English sources use k instead.
Heat moves in three ways: conduction, convection and radiation. Thermal conductivity describes conduction only.
In metals, free electrons carry the heat. That is why metals that conduct electricity well also tend to conduct heat well.
How do you read the unit W/(m·K)?
W/(m·K) is read "watts per metre per kelvin".
The watt is the amount of heat flowing per second. The metre combines the thickness and the area of the plate, and the kelvin is the temperature difference.
A step of one kelvin is the same size as a step of one degree Celsius. For a temperature difference, 1 K and 1 °C are the same.
So W/(m·K) and W/(m·°C) give the same number.
How do you convert units of thermal conductivity?
Multiply a value in kcal/(m·h·°C), common in older books, by 1.163 to get W/(m·K).
| Unit | In W/(m·K) | Where you see it |
|---|---|---|
| W/(m·K) | 1 | Current data sheets (SI) |
| W/(m·℃) | 1 | Tables that write the temperature difference in °C |
| mW/(m·K) | 0.001 | Gas tables |
| kcal/(m·h·℃) | 1.163 | Older building and engineering books |
| cal/(cm·s·℃) | 418.68 | Older science and chemistry books |
Source: Unit definitions (1 kcal = 4,186.8 J, 1 h = 3,600 s)
The kcal is an amount of heat and h is one hour. One hour is 3,600 seconds, which is where the factor comes from.
Gas tables often use mW/(m·K), a thousandth of the SI unit. Check the unit before you compare.
What is the formula for heat flow by conduction?
Heat flow through a plate equals thermal conductivity × area × temperature difference ÷ thickness.
Take a glass plate 1 cm thick and 1 m² in area, with a 10 °C difference between its faces.
With the glass value from the building table, the formula gives about 1,000 W.
That figure covers the glass alone. In a real window, the thin layers of air at each surface also resist heat, so the actual heat flow is much smaller.
Thermal conductivity alone does not tell you how well a window or wall insulates. Surface heat transfer is explained in a later section.
What is the thermal conductivity of metals?
Among pure metals, silver is highest, followed by copper, gold and aluminium.
| Metal | Thermal cond. (W/(m·K)) | Temp. | Note |
|---|---|---|---|
| Silver | 429 | Room temp. (about 25 °C) | Highest among metals |
| Copper | 386–402 | Room temp. (about 25 °C) | Depends on purity |
| Gold | 318 | Room temp. (about 25 °C) | |
| Aluminium | 226–237 | Room temp. (about 25 °C) | Varies by report and sample |
| Tungsten | 169–176 | Room temp. (about 25 °C) | |
| Molybdenum | 138 | Room temp. (about 25 °C) | |
| Zinc | 116 | Room temp. (about 25 °C) | |
| Nickel | 90.9 | Room temp. (about 25 °C) | |
| Iron (pure) | 72–80.4 | Room temp. (about 25 °C) | Steel is lower |
| Platinum | 71.6 | Room temp. (about 25 °C) | |
| Tin | 66.8 | Room temp. (about 25 °C) | Polycrystalline |
| Lead | 35.4 | 20 °C | |
| Titanium (pure) | 21.9 | Room temp. (about 25 °C) | Polycrystalline |
Source: AIST (National Institute of Advanced Industrial Science and Technology, Japan), "Thermal conductivity of metals", Distributed Thermophysical Property Database / NIST, "Material Properties: Lead" (cryogenic material properties; curve fit evaluated at 20 °C)
The values are AIST's room-temperature values (about 25 °C).
Where several measurements exist, the table shows the range. Copper and aluminium vary with purity and with the sample measured.
Which metal has the highest thermal conductivity?
Silver has the highest thermal conductivity of any metal, with copper second.
Silver is expensive, so parts that need to shed heat are usually made of copper or aluminium.
What is the order of metals by thermal conductivity?
From highest: silver, copper, gold, aluminium.
Tungsten, molybdenum, zinc, nickel and iron follow. Titanium has the lowest value of the metals in the table.
Pure aluminium conducts heat about three times better than pure iron. Heat spreads quickly across an aluminium pan.
To compare how heavy the same metals are, see the density of metals chart. Their melting temperatures are in the melting points of metals chart.
Why do alloys have a range of thermal conductivity?
An alloy's thermal conductivity depends on what is added, how much, and how it was heat-treated, so it has no single value.
| Alloy | Thermal cond. (W/(m·K)) | Temp. | What it is |
|---|---|---|---|
| Oxygen-free copper (C10200) | 397 | 20 °C | Copper, 99.96% or purer |
| Aluminium 1100 | 212 | 20 °C | Commercially pure (99%+) |
| Aluminium 6063-T5 | 201 | 20 °C | Extrusions such as window frames |
| Aluminium 3003 | 177 | 20 °C | Al-Mn sheet |
| Aluminium 6061-T6 | 154 | 20 °C | Structural alloy |
| Aluminium 5083 | 118 | 20 °C | High-Mg marine alloy |
| Carbon steel | 41 | Room temp. | Iron with carbon |
| Stainless steel 430 | 26.0 | Not stated | Ferritic (magnetic) |
| Stainless steel 410 | 24.2 | Not stated | Martensitic (blades) |
| Stainless steel 304 | 16.3 | Not stated | Austenitic (18-8) |
| Stainless steel 316 | 16.3 | Not stated | Austenitic with Mo |
| Stainless steel 304 (NIST) | 15.1 | 20 °C | Same grade, another source |
| Stainless steel 310S | 13.8 | Not stated | Heat-resistant austenitic |
| Titanium alloy Ti-6Al-4V | 7.4 | 20 °C | Grade 5 titanium |
Source (10)
- NIST, "Material Properties: OFHC Copper (UNS C10100/C10200)" (cryogenic material properties; curve fit evaluated at 20 °C)
- NIST, "Material Properties: 1100 Aluminum" (cryogenic material properties; curve fit evaluated at 20 °C)
- NIST, "Material Properties: 6063-T5 Aluminum" (cryogenic material properties; curve fit evaluated at 20 °C)
- NIST, "Material Properties: 3003-F Aluminum" (cryogenic material properties; curve fit evaluated at 20 °C)
- NIST, "Material Properties: 6061-T6 Aluminum" (cryogenic material properties; curve fit evaluated at 20 °C)
- NIST, "Material Properties: 5083 Aluminum" (cryogenic material properties; curve fit evaluated at 20 °C)
- Kyocera, "Fine ceramics and heat 3: thermal conductivity" (measured to JIS R 1611)
- Nippon Steel, "Stainless Steel Cold Rolled Sheets" catalog (S008, Aug. 2025)
- NIST, "Material Properties: 304 Stainless (UNS S30400)" (cryogenic material properties; curve fit evaluated at 20 °C)
- NIST, "Material Properties: Ti-6Al-4V" (cryogenic material properties; curve fit evaluated at 20 °C)
Adding other elements to a metal gets in the way of the electrons that carry heat. Alloys therefore conduct less than the pure metal they are based on.
The stainless steel and aluminium alloy values come from different sources: Nippon Steel's catalog for stainless steel and NIST for the aluminium alloys.
For the same grade 304, Nippon Steel and NIST give slightly different values, because the temperature and the samples differ.
Compare alloys by grade or alloy number and by source. Comparing by name alone can mislead you.
What is the thermal conductivity of stainless steel?
Stainless steel 304 is about 16 W/(m·K) and 430 is about 26 W/(m·K).
Stainless steel conducts heat worse than iron: about one fifth of pure iron. It is also less than half of carbon steel.
Stainless steel contains a lot of chromium and nickel, which makes heat flow harder. In a stainless pan, heat tends to stay where the flame touches.
Austenitic grades such as 304 are lower than ferritic grades such as 430.
What is the thermal conductivity of aluminium?
Pure aluminium is about 230 W/(m·K); the alloys in the table range from about 120 to 210.
Commercially pure 1100 is high, while 5083, rich in magnesium, is about half that. Alloy 6063, used for window frames, sits in between.
When you compare aluminium products, check the alloy number (1100, 5052, 6063 and so on). No primary source for 5052 could be confirmed, so it is not in the table.
What is the thermal conductivity of copper?
Copper is about 390 to 400 W/(m·K), second only to silver.
Oxygen-free copper (C10200) is almost the same. Brass contains a lot of zinc and is much lower.
No primary source for brass could be confirmed, so it is not in the table.
What is the thermal conductivity of titanium?
Pure titanium is about 22 W/(m·K), and the titanium alloy Ti-6Al-4V is about 7.
Titanium conducts heat poorly for a metal, and the alloy is lower even than stainless steel.
That is why the rim of a titanium mug stays cooler. For how metals compare in hardness, see the Mohs hardness chart.
Does thermal conductivity change with temperature?
Yes. Water's thermal conductivity rises by about 20% between 0 °C and 80 °C.
| Substance | Thermal cond. (W/(m·K)) | Temp. |
|---|---|---|
| Water | 0.556 | 0 °C |
| Water | 0.598 | 20 °C |
| Water | 0.629 | 40 °C |
| Water | 0.651 | 60 °C |
| Water | 0.667 | 80 °C |
Source: NIST Chemistry WebBook, "Thermophysical Properties of Fluid Systems" (isobaric data at 0.101325 MPa)
How much a value changes depends on the material. Metals also change when the temperature moves a long way.
Gases conduct better as they get hotter. For furnaces or freezers, use the value at the working temperature.
Before using a value from a chart, check that its temperature is close to your conditions.
What is the thermal conductivity of building materials?
Concrete is about 1.6, glass 1.0 and wood about 0.12 W/(m·K).
| Material | Thermal cond. (W/(m·K)) | Group |
|---|---|---|
| Steel | 55 | Metal |
| Aluminium | 210 | Metal |
| Copper | 370 | Metal |
| Stainless steel | 15 | Metal |
| Rock | 3.1 | Stone, soil |
| Soil | 1.0 | Stone, soil |
| Concrete | 1.6 | Concrete |
| Cement mortar | 1.5 | Concrete |
| AAC (autoclaved aerated concrete) | 0.19 | Concrete |
| Tile | 1.3 | Walls, boards |
| Glass | 1.0 | Walls, boards |
| Roof tile | 1.0 | Walls, boards |
| Clay wall | 0.69 | Walls, boards |
| Brick | 0.64 | Walls, boards |
| Gypsum board | 0.22 | Walls, boards |
| Plywood | 0.16 | Wood |
| Natural wood | 0.12 | Wood |
| MDF | 0.12 | Wood |
| FRP (fibre-reinforced plastic) | 0.26 | Floors |
| Vinyl flooring | 0.19 | Floors |
| Tatami | 0.15 | Floors |
| Carpet | 0.08 | Floors |
Source: IBECs, "Thermal constants of materials" (from SHASE, "HASPEE", 2012)
These are typical values used to calculate heating and cooling loads in buildings. The same material varies with density and moisture.
The metal values in this table are lower than the measurements for pure metals. They are design values for buildings, so do not mix them with the pure-metal table.
Wood conducts less heat than concrete because its cells hold air.
What is the thermal conductivity of insulation?
Insulation is about 0.02 to 0.05 W/(m·K), a few tens of times lower than concrete.
| Insulation | Thermal cond. (W/(m·K)) | Type |
|---|---|---|
| Glass wool, 10 kg/m³ | 0.050 | Fibrous |
| Glass wool, 16 kg/m³ | 0.045 | Fibrous |
| Glass wool, 24 kg/m³ | 0.038 | Fibrous |
| Glass wool, 32 kg/m³ | 0.036 | Fibrous |
| High-performance glass wool, 16 kg/m³ | 0.038 | Fibrous |
| High-performance glass wool, 24 kg/m³ | 0.036 | Fibrous |
| Rock wool (mat) | 0.038 | Fibrous |
| Blown cellulose fibre, 25 kg/m³ | 0.040 | Fibrous |
| EPS (bead foam), grade 4 | 0.043 | Plastic foam |
| EPS (bead foam), special grade | 0.034 | Plastic foam |
| XPS (extruded), type 1 | 0.040 | Plastic foam |
| XPS (extruded), type 2 | 0.034 | Plastic foam |
| XPS (extruded), type 3 | 0.028 | Plastic foam |
| Rigid polyurethane foam, type 2-1 | 0.023 | Plastic foam |
| Phenolic foam, type 1-1 | 0.022 | Plastic foam |
Source: IBECs, "Thermal constants of materials" (from SHASE, "HASPEE", 2012)
"16 kg/m³" for glass wool is its density. For the same kind of glass wool, the denser product has the lower value.
Among plastic foams, phenolic foam and rigid polyurethane foam have the lowest values.
The grade names follow the Japanese Industrial Standards in force when the table was compiled. For a real product, check the thermal conductivity printed on the bag or in the catalog.
Is lower thermal conductivity better for insulation?
Yes. At the same thickness, insulation with a lower value lets less heat through.
Insulation is also rated by thermal resistance, which is the thickness in metres divided by the thermal conductivity.
For example, 100 mm of 16 kg/m³ glass wool has a thermal resistance of about 2.2 m²·K/W. To match that with concrete, you would need about 3.6 m of it.
Compare insulation by thermal conductivity and thickness together. A slightly higher value can be made up for by a thicker layer.
What is the thermal conductivity of liquids and gases?
Water is about 0.6 and air about 0.026 W/(m·K), so water conducts about 23 times better than air.
| Substance | Thermal cond. (W/(m·K)) | Temp. | State |
|---|---|---|---|
| Water | 0.598 | 20 °C | Liquid |
| Steam | 0.0246 | 100 °C | Gas |
| Hydrogen | 0.183 | 20 °C | Gas |
| Helium | 0.154 | 20 °C | Gas |
| Air | 0.0264 | 27 °C | Gas |
| Oxygen | 0.0259 | 20 °C | Gas |
| Nitrogen | 0.0255 | 20 °C | Gas |
| Argon | 0.0175 | 20 °C | Gas |
| Carbon dioxide | 0.0163 | 20 °C | Gas |
Source: NIST Chemistry WebBook, "Thermophysical Properties of Fluid Systems" (isobaric data at 0.101325 MPa) / E. W. Lemmon and R. T. Jacobsen (2004), "Viscosity and Thermal Conductivity Equations for Nitrogen, Oxygen, Argon, and Air", Int. J. Thermophys. 25 (NIST)
Most gases are between 0.01 and 0.03. Hydrogen and helium are higher because their light molecules move fast.
What is the thermal conductivity of air?
Air is about 0.026 W/(m·K) at 27 °C and 1 atm.
Air conducts heat worse than almost any solid. Most insulation works by trapping still air in small bubbles or between fibres.
When air moves, though, convection carries heat. A wide air gap does not behave as the conductivity value suggests.
What is the thermal conductivity of water?
Water is about 0.6 W/(m·K) at 20 °C.
Water conducts heat more than 20 times better than air. That is one reason cold water feels colder than air at the same temperature.
What is the thermal conductivity of ceramics and plastics?
Fine ceramics range widely from 3 to 150 W/(m·K), while plastics are low, around 0.2 to 0.4.
| Material | Thermal cond. (W/(m·K)) | Temp. | Type |
|---|---|---|---|
| Aluminium nitride | 150 | Room temp. | Fine ceramic |
| Silicon carbide | 60 | Room temp. | Fine ceramic |
| Alumina | 32 | Room temp. | Fine ceramic |
| Silicon nitride | 20 | Room temp. | Fine ceramic |
| Zirconia | 3 | Room temp. | Fine ceramic |
| Nylon (polyamide) | 0.34 | 20 °C | Plastic |
| PTFE (Teflon) | 0.27 | 20 °C | Plastic |
| Polyimide (Kapton) | 0.19 | 20 °C | Plastic |
Source (4)
- Kyocera, "Fine ceramics and heat 3: thermal conductivity" (measured to JIS R 1611)
- NIST, "Material Properties: Polyamide (Nylon)" (cryogenic material properties; curve fit evaluated at 20 °C)
- NIST, "Material Properties: Teflon" (cryogenic material properties; curve fit evaluated at 20 °C)
- NIST, "Material Properties: Polyimide (Kapton)" (cryogenic material properties; curve fit evaluated at 20 °C)
Aluminium nitride and silicon carbide do not conduct electricity but do conduct heat well. That makes them useful for drawing heat away from semiconductors.
Zirconia conducts heat poorly for a ceramic. It is used where heat must be blocked, such as furnace walls.
Plastics are a few tens of times lower even than stainless steel. That is why pan handles are often plastic.
How does thermal conductivity differ from the heat transfer coefficient?
Thermal conductivity describes heat flow inside a material; the heat transfer coefficient describes heat flow between a surface and the air or water around it.
| Thermal conductivity | Heat transfer coefficient | U-value | |
|---|---|---|---|
| What it describes | Heat flow inside a material | Between a surface and a fluid | Through a whole wall or window |
| Unit | W/(m·K) | W/(m²·K) | W/(m²·K) |
| Depends on | Material and temperature | Wind, surface orientation | Materials, thickness, surfaces |
| Typical use | Comparing materials | Designing cooling | Rating a home's insulation |
The heat transfer coefficient is not a property of the material. The same plate has a larger value in a strong wind.
The U-value describes how much heat passes through a whole wall or window. Home insulation is usually compared by this value.
What happens when thermal conductivity is high or low?
High thermal conductivity spreads heat quickly; low thermal conductivity keeps heat where it is.
High values suit jobs where you want to spread or remove heat. Low values suit jobs where you want to keep heat in or out.
| Thermal conductivity | Good for | Examples |
|---|---|---|
| High | Spreading or removing heat | Copper pans, aluminium heat sinks, aluminium nitride substrates |
| Medium | Balancing strength and heat | Steel structures, stainless steel sinks |
| Low | Keeping heat in or out | Insulation, plastic handles, wooden floors |
How a frying pan heats depends on its thickness and weight as well as its thermal conductivity. Look at the material and the thickness together.
Frequently asked questions about thermal conductivity
Which substance has the highest thermal conductivity?
According to Kyocera, diamond has the highest thermal conductivity of any substance at room temperature.
No primary source for diamond's value could be confirmed, so it is not in the tables. Among metals, silver is highest.
Does stainless steel conduct heat better than iron?
No. Stainless steel conducts heat worse than iron.
Stainless steel 304 is about one fifth of pure iron.
How many times better does aluminium conduct heat than iron?
Pure aluminium conducts about three times better than pure iron.
Comparing aluminium alloys with carbon steel, the gap is about three to five times.
What is the symbol for thermal conductivity?
The symbol λ (lambda) is common.
Many English sources write k. Either way, the unit is W/(m·K).
How does thermal conductivity differ from specific heat?
Thermal conductivity is how easily heat moves; specific heat is how much heat it takes to warm something up.
Specific heat is the heat needed to raise 1 g by 1 °C. A material with high conductivity can still warm slowly if its specific heat is large.
How does glass compare with stainless steel?
In the building table, glass is 1.0 and stainless steel is 15 W/(m·K).
Stainless steel conducts heat about 15 times better than glass.
Sources
- Thermal conductivity of metals (AIST Distributed Thermophysical Property Database)
- Stainless Steel Cold Rolled Sheets catalog S008 (Nippon Steel, Aug. 2025)
- Material Properties (NIST cryogenic materials: 304 stainless, aluminium 1100/3003/5083/6061/6063, OFHC copper, Ti-6Al-4V, lead, nylon, PTFE, polyimide)
- Thermophysical Properties of Fluid Systems (NIST Chemistry WebBook)
- E. W. Lemmon and R. T. Jacobsen (2004), Viscosity and Thermal Conductivity Equations for Nitrogen, Oxygen, Argon, and Air, International Journal of Thermophysics 25 (value for air)
- Thermal constants of materials (IBECs, from SHASE, "HASPEE", 2012)
- Fine ceramics and heat 3: thermal conductivity (Kyocera)
