ORIGINAL: nick_75au
Aluminium (205) about 1.5 times better than brass(109-125), copper(386) nearly 2 times better than aluminium. If you can afford it, diamond(1000 impure to 2500 pure), water (0.6) air (0.026). Im not exactly sure of what the numbers mean but the higher the better.
http://en.wikipedia.org/wiki/Thermal_conductivity
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