High Conductivity Materials: Thermal Values and How to Choose
The materials with the highest thermal conductivity are carbon-based: graphene and diamond. Among practical metals, silver and copper lead at roughly 400 W/(m·K), followed by gold and aluminum. Which one you should pick depends on more than the headline number. Cost, electrical isolation, thermal expansion and service temperature decide most real designs.
This guide ranks the materials, explains the difference between thermal and electrical conductivity (the two are often mixed up in search results), covers low-expansion options, and finishes with a way to shortlist a material for a high-temperature part.
TL;DR
Silver and copper are the best common metals for moving heat, at roughly 400 W/(m·K) each. Aluminum is about half that but far lighter and cheaper.
Diamond (about 1,000 W/(m·K) or more) and graphene (several thousand in the lab) lead overall. Diamond is also an electrical insulator, which is why it is used under power devices.
Aluminum nitride gives 100 to 180 W/(m·K) with electrical insulation and ceramic stability, up to 1750°C maximum application temperature.
High conductivity and low thermal expansion rarely come together in one cheap material. Iron-nickel alloys and cordierite ceramics are low-expansion, but not high-conductivity.
Always check the whole system: interfaces and geometry often matter more than the bulk material.
Table of Contents
Which materials conduct heat best?
Thermal conductivity (κ, in W/(m·K)) tells you how much heat flows through a unit of material for a given temperature gradient. Ranked from the top, the picture looks like this.
Material | Thermal conductivity | Notes |
Graphene (in-plane, lab) | 4,840 to 5,300 W/(m·K) | Measured on suspended samples; not a bulk engineering material |
CVD diamond | 1,000+ W/(m·K) | Electrical insulator |
Silver | about 408 W/(m·K) | Highest of the common metals |
Copper | about 394 W/(m·K) | Standard for heat spreaders |
Gold | about 296 W/(m·K) | Used where corrosion resistance matters |
Aluminum | about 218 W/(m·K) | Light, easy to extrude and machine |
Aluminum nitride | 100 to 180 W/(m·K) | Ceramic, electrically insulating |
Sintered silicon nitride | 15 to 45 W/(m·K) | Tough, high-temperature ceramic |
The metal values come from a materials table published by Applied Thin-Film Products, which lists silver at 4.08 W/(cm·°C), copper at 3.94, gold at 2.96 and aluminum at 2.18. Multiply by 100 to get W/(m·K). Other references put silver and copper slightly higher, at 429 and 401 W/(m·K). That spread is normal: purity, grain structure and temperature all move the number, so treat a handbook value as a starting point, not a guarantee.
Metals: the workhorses
Silver is the best metal, but its cost keeps it out of most thermal hardware. Copper is almost as good and is the default for cold plates, heat pipes and spreader blocks. Aluminum carries about half the conductivity of copper but is much lighter, which is why it dominates extruded heat sinks. If you are choosing between the two for a fin stack, our guide to materials for heat sinks works through the trade-offs of weight, cost and manufacturability.
Carbon materials: the extreme end
Diamond is listed at about 1,000 W/(m·K), and isotopically enriched diamond is reported far higher in the literature. Synthetic CVD diamond is sold commercially for thermal management: one manufacturer’s polycrystalline diamond plate is specified above 1,000 W/(m·K) at 293 K, with a bulk resistivity of 1×10^12 Ω·cm, and is aimed at high-power RF, optoelectronics and high-voltage semiconductor devices. The cited 10×10×0.30 mm plate is priced at $160, which tells you why diamond is reserved for hot spots where nothing else works.
Graphene’s headline values are the highest of any known material, but a single atomic layer cannot carry heat the way a solid block does. In practice it shows up in films, coatings and composites, where the effective conductivity is much lower than the laboratory figure.
Ceramics: conductive and insulating at once
Most ceramics are poor conductors, but a few are exceptions. According to the German technical ceramics information center, aluminum nitride offers 100 to 180 W/(m·K) with a maximum application temperature of 1750°C. That combination of heat spreading and electrical insulation makes it a common substrate under power electronics. Sintered silicon nitride sits lower, at 15 to 45 W/(m·K), but is chosen for toughness at the same maximum temperature.
Thermal conductivity vs. electrical conductivity
Many pages ranking for this keyword are really about electrical conductivity: silver, copper, gold and aluminum in a resistivity table. The two properties are related in metals, but they are not the same thing.
Electrical conductivity (σ) measures how well a material carries current. Resistivity (ρ) is its reciprocal, ρ = 1/σ. Thermal conductivity (κ) measures heat conduction. Cambridge’s DoITPoMS teaching material covers the definitions and units.
In metals, free electrons carry both heat and charge, which is why the ranking is similar. The Wiedemann-Franz law states that the ratio κ/σ is proportional to temperature.
The same table that gives silver and copper their thermal ranking lists electrical conductivity at 6.090×10^7 and 5.800×10^7 S/m respectively, with gold at 4.257×10^7 and aluminum at 3.538×10^7 S/m.
The relationship breaks down outside metals. Diamond is an electrical insulator yet one of the best thermal conductors, because in non-metals heat travels as lattice vibrations (phonons), not free electrons. That is why diamond and aluminum nitride can sit between a chip and a heat sink without shorting anything.
Temperature matters too. As HyperPhysics explains, rising temperature increases electron scattering by lattice vibrations, which lowers electrical conductivity in metals. Take handbook values at room temperature as a baseline and check what happens at your operating point.
Low thermal expansion materials
A high-conductivity part that grows or shrinks too much will crack solder joints, warp substrates or change clearances. The coefficient of thermal expansion α relates the change in length (Δl) to the change in temperature (ΔT). Low-expansion materials fall into two main families, as summarized in a 2025 review of thermal and magnetic materials:
Iron-nickel alloys have a coefficient of roughly 1.5 × 10^-6 K^-1 and are used in precision aerospace components that need stability across wide temperature ranges.
Ceramics such as cordierite (C 410) have a mean linear expansion coefficient of 1 to 3 × 10^-6 K^-1 between 30 and 100°C.
The catch is that neither family is a strong conductor. Cordierite is a thermal insulator by comparison with the metals above, and iron-nickel alloys conduct heat far worse than copper. When a design needs both, engineers usually combine materials: a conductive layer (copper, aluminum nitride or diamond) bonded to a matched, low-expansion carrier, and they size the bond line to absorb the remaining mismatch.
There is also a reminder in the gas turbine literature that low expansion is not always the goal. A review of materials selection in gas turbine design notes that low-expansion alloys often give up other properties such as corrosion resistance, and that for most turbine components low expansion is not an important requirement, though controlling it can improve engine performance.
Materials for high-temperature applications
Service temperature narrows the field before conductivity is even considered. In gas turbine design, common alloys are generally limited to service temperatures below 750°C, which complicates their use in the hottest sections, according to the same gas turbine review. Technical ceramics step in higher up: they often combine dimensional stability, high melting points and good thermal shock resistance.
Three properties interact in a hot part:
Service temperature decides which families are even allowed.
Thermal conductivity controls how well the part cools itself and how steep the temperature gradients inside it become.
Thermal expansion controls the stresses those gradients create and the clearances you have to leave.
One caution from the ceramics industry applies to every datasheet: published values are averages, and figures measured on standard test specimens do not transfer easily to other shapes and sizes. Manufacturer-specific data is the safer input for a final design. For a deeper look at how heat moves at these temperatures, including radiation, see our article on high-temperature heat transfer and our overview of high-temperature thermal analysis methods and limits.
A practical way to shortlist a material
Use a short, repeatable filter instead of picking the biggest κ on the table.
Set the temperature window. If the part sees more than about 750°C, many common alloys are out and ceramics or refractory options come in.
Decide whether the material must insulate electrically. If yes, copper and aluminum are out, and aluminum nitride or diamond move up.
Check expansion against the neighbors. Compare α with the chip, substrate or housing it touches, not in isolation.
Check weight, cost and manufacturability. Aluminum extrudes cheaply; diamond is bought in millimeter-scale plates.
Estimate the temperature drop. For one-dimensional conduction the drop is Q·L/(κ·A). A quick calculation often shows that a 10 percent better material changes little while a thinner interface changes a lot.
That last point is why interfaces deserve as much attention as the bulk. A superb spreader with a poor joint to the heat source still runs hot. Our guides on thermal interface materials and practical TIM selection cover that part of the stack.
A worked comparison
Take a 10 mm thick slab with a 1,000 mm² cross-section carrying 50 W. Using Q·L/(κ·A) with L = 0.010 m and A = 0.001 m², the temperature drop across the slab is 500/κ kelvin. With copper near 394 W/(m·K) that is about 1.3 K. With aluminum near 218 W/(m·K) it is about 2.3 K. With aluminum nitride at 100 W/(m·K) it is 5 K, and at 180 W/(m·K) about 2.8 K. The bulk differences are a few kelvin. A poorly wetted interface can easily cost more than that, so the material choice only matters once the joints are handled.
Our perspective
Most thermal material questions we see from engineers and students start with a table and end with a surprise. The table said copper, but the part needed electrical isolation. The table said aluminum nitride, but the expansion mismatch cracked the joint. A property list is only one input to a model, and the useful step is running the numbers for your own geometry, loads and temperatures.
That is the reason we built our toolkit around conduction, convection and radiation in one place, with variable material properties and a built-in property database. Conductivity changes with temperature, so a single handbook value can mislead you, and checking a few candidate materials across your real temperature range takes minutes instead of days. Start with the material table, then let the model tell you whether the difference matters.
— Joel
Try the numbers on your own design
If you are comparing copper, aluminum or a ceramic for a specific part, the Jewlz Engineering Toolkit lets you model conduction, convection and radiation together with temperature-dependent properties, as a downloadable Excel-based tool. Basic tools are free, and the premium Thermalysis Toolkit is a monthly subscription. Our thermal analysis page shows what each calculation covers.
FAQ
What is the most thermally conductive material?
Graphene has the highest reported values, around 4,840 to 5,300 W/(m·K) in laboratory measurements, and isotopically enriched diamond is also reported very high. For bulk engineering use, CVD diamond at 1,000+ W/(m·K) is the top commercial option, followed by silver and copper.
Which metal conducts heat best?
Silver, at about 408 W/(m·K) in one common table, with copper close behind at about 394. Copper is used far more often because it costs much less. Aluminum is lower at about 218 W/(m·K) but is lighter and easier to form.
Are good electrical conductors always good thermal conductors?
In metals, mostly yes, because free electrons carry both heat and charge, and the Wiedemann-Franz law links the two. Outside metals the rule fails: diamond and aluminum nitride conduct heat well but are electrical insulators.
What materials have both low thermal expansion and good conductivity?
No common material excels at both. Iron-nickel alloys (about 1.5 × 10^-6 K^-1) and cordierite ceramics (1 to 3 × 10^-6 K^-1) expand very little but conduct modestly. Designers usually pair a conductive layer with a low-expansion carrier. Aluminum nitride is a useful middle ground when you need insulation, conductivity and stability.
Sources
Recommended
Comments