The thermal conductivity of the heatsink's material has a major impact on cooling performance. Thermal conductivity is measured in W/mK; higher values mean better conductivity.

As a rule of thumb, materials with a high electrical conductivity also have a high thermal conductivity.

Alloys have lower thermal conductivity than pure metals, but may have better mechanical or chemical (corrosion) properties.

The following materials are commonly used for heatsinks:

• Aluminum

  It has a thermal conductivity of 205W/mK, which is good (as a comparison: steel has about 50W/mK). The production of aluminum heatsinks is inexpensive; they can be made using extrusion Due to its softness, aluminum can also be milled quickly; die-casting and even cold forging are also possible (see part 2 of this guide for more information about production methods). Aluminum is also very light (thus, an aluminum heatsink will put less stress on its mounting when the unit is moved around).

• Copper

  Copper’s thermal conductivity is about twice as high as aluminum - almost 400W/mK. This makes it an excellent material for heatsinks; but its disadvantages include high weight, high price, and less choice as far as production methods are concerned. Copper heatsinks can be milled, die-cast, or made of copper plates bonded together; extrusion is not possible.

• Aluminum and Copper Bonded Together

  To combine the advantages of aluminum and copper, heatsinks can be made of aluminum and copper bonded together. Here, the area in contact with the heat source is made of copper, which helps lead the heat away to the outer parts of the heatsink. The first heatsink for PC CPUs with an embedded copper piece was the Alpha P7125 (for first-generation Slot A Athlon CPUs). Keep in mind that a copper embedding is only useful if it is tightly bonded to the aluminum part for good thermal transfer. This is not always the case, especially not with inexpensive coolers. If the thermal transfer between the copper and the aluminum is poor, the copper embedding may do more harm than good.

• Silver

  Silver has an even higher thermal conductivity than copper, but only by about 10%. This does not justify the much higher price for heatsink production - however, pulverized silver is a common ingredient in high-end thermal compounds.

Base Plate The copper plate helps spread heat across the base plate.

Heatsink with copper core The copper core helps the heat move to the upper parts of the heatsink.

Heatsink (prototype) with large heat pipe in the center A heat pipe provides substantially better thermal transfer than a solid piece of copper.