# Thermal Conductivity

 Material Thermal conductivity(cal/sec)/(cm2 C/cm) Thermal conductivity(W/m K)* Diamond ... 1000 Silver 1.01 406.0 Copper 0.99 385.0 Gold ... 314 Brass ... 109.0 Aluminum 0.50 205.0 Iron 0.163 79.5 Steel ... 50.2 Lead 0.083 34.7 Mercury ... 8.3 Ice 0.005 1.6 Glass,ordinary 0.0025 0.8 Concrete 0.002 0.8 Water at 20° C 0.0014 0.6 Asbestos 0.0004 0.08 Snow (dry) 0.00026 ... Fiberglass 0.00015 0.04 Brick,insulating ... 0.15 Brick, red ... 0.6 Cork board 0.00011 0.04 Wool felt 0.0001 0.04 Rock wool ... 0.04 Polystyrene (styrofoam) ... 0.033 Polyurethane ... 0.02 Wood 0.0001 0.12-0.04 Air at 0° C 0.000057 0.024 Helium (20°C) ... 0.138 Hydrogen(20°C) ... 0.172 Nitrogen(20°C) ... 0.0234 Oxygen(20°C) ... 0.0238 Silica aerogel ... 0.003

*Most from Young, Hugh D., University Physics, 7th Ed. Table 15-5. Values for diamond and silica aerogel from CRC Handbook of Chemistry and Physics.

Note that 1 (cal/sec)/(cm2 C/cm) = 419 W/m K. With this in mind, the two columns above are not always consistent. All values are from published tables, but can't be taken as authoritative.

The value of 0.02 W/mK for polyurethane can be taken as a nominal figure which establishes polyurethane foam as one of the best insulators. NIST published a numerical approximation routine for calculating the thermal conductivity of polyurethane at http://cryogenics.nist.gov/NewFiles/Polyurethane.html . Their calculation for freon filled polyurethane of density 1.99 lb/ft3 at 20°C gives a thermal conductivity of 0.022 W/mK. The calculation for CO2 filled polyurethane of density 2.00 lb/ft3 gives 0.035 W/mK .

 Heat conduction discussion Debye Temperature and Thermal Conductivity
Index

Tables

Reference
Young
Ch 15.
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# Wiedemann-Franz Ratio

The ratio between thermal and electrical conductivities of metals can be expressed in terms of the ratio:

which may be called the Wiedemann-Franz Ratio or the Lorenz constant.

 Metal k/sT (10-8WW/K2) Cu 2.23 Ag 2.31 Au 2.35 Zn 2.31 Cd 2.42 Sn 2.52 Mo 2.61 Pb 2.47 Pt 2.51
 Heat conduction discussion Wiedemann-Franz Law
Index

Tables

Reference
Blatt
Section 13.2
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