Silver has the highest thermal conductivity of any metal, measured at 406 W/mK at room temperature. It edges out copper (385 W/mK) and gold (314 W/mK), making it the most efficient metal for transferring heat. That said, silver’s lead over copper is relatively slim, which explains why copper dominates most real-world heat transfer applications.
Top 5 Most Thermally Conductive Metals
The ranking of metals by thermal conductivity at room temperature is well established:
- Silver: 406 W/mK
- Copper: 385 W/mK
- Gold: 314 W/mK
- Aluminum: 237 W/mK
- Tungsten: approximately 170 W/mK
Silver beats copper by only about 5%. That small margin is the reason copper shows up in heat sinks, cookware, and electronics far more often. Silver costs roughly 50 to 80 times more than copper per kilogram, so the tiny performance advantage rarely justifies the price. Gold, despite its excellent conductivity, is even more expensive and is reserved for specialized electronics where corrosion resistance matters as much as heat transfer.
Aluminum sits noticeably lower on the list but weighs about a third as much as copper. When you compare conductivity per unit of weight rather than per unit of volume, aluminum actually outperforms copper, which is why it’s the go-to choice for aircraft heat exchangers, automotive radiators, and lightweight heat sinks.
Why Free Electrons Make Metals Good Conductors
Metals conduct heat so well because their atoms share a sea of loosely bound electrons that move freely through the material. When one end of a metal bar gets hot, those free electrons pick up kinetic energy and carry it rapidly toward the cooler end. Research confirms that electrons dominate thermal flow inside metals, contributing far more to heat transfer than vibrations of the metal’s atomic lattice.
This same pool of free electrons is also responsible for electrical conductivity. That’s why the best electrical conductors (silver, copper, gold) are also the best thermal conductors, in almost the same order. The relationship between a metal’s ability to conduct heat and electricity is consistent enough that physicists treat it as a fundamental property of metals.
How Temperature Changes the Picture
Thermal conductivity isn’t a fixed number. It shifts with temperature, sometimes dramatically. Bulk silver actually gets better at conducting heat as it cools down. At around 20 K (roughly negative 253°C), silver’s thermal conductivity jumps to more than ten times its room temperature value. At extremely low temperatures, there are fewer atomic vibrations to scatter electrons, so heat flows through the metal with very little resistance.
In the other direction, heating a metal generally reduces its thermal conductivity. The atoms vibrate more intensely, creating more obstacles for the electrons carrying heat. For most practical purposes, room temperature values are what matter, but engineers designing cryogenic equipment or high-temperature industrial systems need to account for these shifts.
How Alloying Reduces Thermal Conductivity
Pure metals conduct heat far better than alloys. When you mix other elements into a metal, the foreign atoms disrupt the orderly crystal structure and scatter the free electrons that carry heat. The drop can be steep. Pure aluminum conducts at 237 W/mK, but common aluminum casting alloys used in car engines fall to 96 or 109 W/mK, less than half the pure metal’s value.
Even small additions matter. Just 1% silicon dissolved in aluminum reduces its thermal conductivity by about 54 W/mK. One percent magnesium costs about 36 W/mK, and 1% copper about 17 W/mK. Some trace elements are even more disruptive: adding just 0.1% chromium or vanadium to an aluminum-silicon alloy can cut thermal conductivity by 12 to 19 W/mK.
The state of the alloying element matters too. Elements dissolved evenly throughout the metal (in solid solution) cause more damage to conductivity than the same elements clustered into tiny particles within the metal. Heat treatments that push alloying elements out of solution and into precipitates can recover a significant portion of the lost conductivity, sometimes 40 to 70 W/mK worth. This is why heat treatment schedules for aluminum alloys are designed with thermal performance in mind, not just strength.
How Silver Compares to Non-Metal Conductors
Silver holds the crown among metals, but it doesn’t come close to certain non-metallic materials. Diamond conducts heat at up to 2,500 W/mK at room temperature, more than six times silver’s value. Diamond has no free electrons to work with. Instead, its carbon atoms are locked in an exceptionally rigid crystal lattice, and vibrations travel through it with almost no energy loss.
Graphene pushes even further. Measurements of single-layer graphene suspended in air have recorded thermal conductivity between 4,840 and 5,300 W/mK, roughly 13 times higher than silver. That figure drops at higher temperatures (to around 1,200 to 1,400 W/mK at 500 K) and drops further when graphene is layered or placed on a substrate, but it still holds the record for the highest thermal conductivity of any known material.
These materials aren’t practical replacements for metals in most situations. Diamond is expensive and difficult to shape, and graphene conducts heat brilliantly in two dimensions but not through its thickness. For bulk heat transfer in everyday products, silver and copper remain the practical leaders. But in specialized applications like semiconductor cooling and high-power electronics, diamond composites and graphene-based materials are increasingly finding a role where metals alone can’t keep up.