Table 4–7. Thermal conductivity of selected hardwoods and softwoodsa—con.Specific
gravityConductivity
(W m–1K–1 (Btu in. h–1ft–2°F–1))Resistivity
(K m W–1 (h ft^2 °F Btu–1in. –1))
Species Ovendry 12% MC Ovendry 12% MC
Softwoods^
Baldcypress 0.47 0.11 (0.76) 0.13 (0.92) 9.1 (1.3) 7.5 (1.1)
Cedar
Atlantic white 0.34 0.085 (0.59) 0.10 (0.70) 12 (1.7) 9.9 (1.4)
Eastern red 0.48 0.11 (0.77) 0.14 (0.94) 8.9 (1.3) 7.4 (1.1)
Northern white 0.31 0.079 (0.55) 0.094 (0.65) 13 (1.8) 11 (1.5)
Port-Orford 0.43 0.10 (0.71) 0.12 (0.85) 9.8 (1.4) 8.1 (1.2)
Western red 0.33 0.083 (0.57) 0.10 (0.68) 12 (1.7) 10 (1.5)
Yellow 0.46 0.11 (0.75) 0.13 (0.90) 9.3 (1.3) 7.7 (1.1)
Douglas-fir
Coast 0.51 0.12 (0.82) 0.14 (0.99) 8.5 (1.2) 7.0 (1.0)
Interior north 0.50 0.12 (0.80) 0.14 (0.97) 8.6 (1.2) 7.1 (1.0)
Interior west 0.52 0.12 (0.83) 0.14 (1.0) 8.4 (1.2) 6.9 1.0)
Fir
Balsam 0.37 0.090 (0.63) 0.11 (0.75) 11 (1.6) 9.2 (1.3)
White 0.41 0.10 (0.68) 0.12 (0.82) 10 (1.5) 8.5 (1.2)
Hemlock
Eastern 0.42 0.10 (0.69) 0.12 (0.84) 10 (1.4) 8.3 (1.2)
Western 0.48 0.11 (0.77) 0.14 (0.94) 8.9 (1.3) 7.4 (1.1)
Larch, western 0.56 0.13 (0.88) 0.15 (1.1) 7.9 (1.1) 6.5 (0.93)
Pine
Eastern white 0.37 0.090 (0.63) 0.11 (0.75) 11 (1.6) 9.2 (1.3)
Jack 0.45 0.11 (0.73) 0.13 (0.89) 9.4 (1.4) 7.8 (1.1)
Loblolly 0.54 0.12 (0.86) 0.15 (1.0) 8.1 (1.2) 6.7 (0.96)
Lodgepole 0.43 0.10 (0.71) 0.12 (0.85) 9.8 (1.4) 8.1 (1.2)
Longleaf 0.62 0.14 (0.96) 0.17 (1.2) 7.2 (1.0) 5.9 (0.85)
Pitch 0.53 0.12 (0.84) 0.15 (1.0) 8.2 (1.2) 6.8 (0.98)
Ponderosa 0.42 0.10 (0.69) 0.12 (0.84) 10 (1.4) 8.3 (1.2)
Red 0.46 0.11 (0.75) 0.13 (0.90) 9.3 (1.3) 7.7 (1.1)
Shortleaf 0.54 0.12 (0.86) 0.15 (1.0) 8.1 (1.2) 6.7 (0.96)
Slash 0.61 0.14 (0.95) 0.17 (1.2) 7.3 (1.1) 6.0 (0.86)
Sugar 0.37 0.090 (0.63) 0.11 (0.75) 11 (1.6) 9.2 (1.3)
Western white 0.40 0.10 (0.67) 0.12 (0.80) 10 (1.5) 8.6 (1.2)
Redwood
Old growth 0.41 0.10 (0.68) 0.12 (0.82) 10 (1.5) 8.5 (1.2)
Young growth 0.37 0.090 (0.63) 0.11 (0.75) 11 (1.6) 9.2 (1.3)
Spruce
Black 0.43 0.10 (0.71) 0.12 (0.85) 9.8 (1.4) 8.1 (1.2)
Engelmann 0.37 0.090 (0.63) 0.11 (0.75) 11 (1.6) 9.2 (1.3)
Red 0.42 0.10 (0.69) 0.12 (0.84) 10 (1.4) 8.3 (1.2)
Sitka 0.42 0.10 (0.69) 0.12 (0.84) 10 (1.4) 8.3 (1.2)
White 0.37 0.090 (0.63) 0.11 (0.75) 11 (1.6) 9.2 (1.3)
aValues in this table are approximate and should be used with caution; actual conductivities may vary by as
much as 20%. The specific gravities also do not represent species averages.Coefficient of Thermal Expansion
The coefficient of thermal expansion is a measure of the
relative change of dimension caused by temperature change.
The thermal expansion coefficients of completely dry wood
are positive in all directions; that is, wood expands on heat-
ing and contracts on cooling. Limited research has been car-
ried out to explore the influence of wood property variability
on thermal expansion. The thermal expansion coefficient of
ovendry wood parallel to the grain appears to be indepen-
dent of specific gravity and species. In tests of both
hardwoods and softwoods, the parallel-to-grain values
have ranged from about 3.1 to 4.5 × 10-^6 K–1
(1.7 to 2.5 × 10-^6 °F–1).
Thermal expansion coefficients across the grain (radial and
tangential) are proportional to specific gravity. These coeffi-
cients range from about 5 to more than 10 times greater than
the parallel-to-grain coefficients and are of more practical
interest. The radial and tangential thermal expansion coef-
ficients for ovendry wood, ar and at, can be approximatedGeneral Technical Report FPL–GTR– 190