Thermal conductivity of a substance is an intensive property that indicates its ability to conduct heat.

Air and other gases are generally good insulators, in the absence of convection. Light gases, such as hydrogen and helium typically have high thermal conductivity. Dense gases such as xenon have low thermal conductivity. An exception, sulfur hexafluoride, a dense gas, has a relatively high thermal conductivity due to its high heat capacity. Argon, a gas denser than air, is often used in double paned windows to improve their insulation characteristics.

The sources are:

Symbol
$k_{\mathrm{gas}}$
Unit
W/m.K
Formulae
$- 3.322412767 \cdot 10^{-11} \theta_{\mathrm{air}}^{4} - 1.351703529 \cdot 10^{-9} \theta_{\mathrm{air}}^{3} - 1.788037411 \cdot 10^{-7} \theta_{\mathrm{air}}^{2} + 7.278410162 \cdot 10^{-5} \theta_{\mathrm{air}} + 0.0240073953$humid air at 1 atm (Tsilingiris2007)
$1.5207 \cdot 10^{-11} T_{air}^{3} - 4.8574 \cdot 10^{-8} T_{air}^{2} + 0.00010184 T_{air} - 0.00039333$air at 1 bar (Dumas&Trancossi2009)
$\frac{0.002334 T_{air}^{1.5}}{T_{air} + 164.54}$air at 1 bar (UW/MHTL 8406, 1984)
$2.47663035 \cdot 10^{-17} T_{air}^{5} - 1.066657 \cdot 10^{-13} T_{air}^{4} + 1.73550646 \cdot 10^{-10} T_{air}^{3} - 1.4815235 \cdot 10^{-7} T_{air}^{2} + 0.00012598485 T_{air} - 0.002276501$dry air at 1 atm (Irvine&Liley1984)
$2.43 E + 6.63 \cdot 10^{-5} \theta_{\mathrm{gas}} - 2$N2 (Vermeer1983)
$1.17 E + 6.2 \cdot 10^{-5} \theta_{\mathrm{gas}} - 2$SF6 (Vermeer1983)
$\frac{0.0241059 T_{\mathrm{gas}}^{3} + 77.7891 T_{\mathrm{gas}}^{2} - 18539.4 T_{\mathrm{gas}} + 1461860}{T_{\mathrm{gas}}^{2} + 505.67 T_{\mathrm{gas}} + 29661.7}$SF6 (Assael2012)
$8.075 \cdot 10^{-5} T_{\mathrm{gas}} - 0.007302$CO2 (linear interpolation)
Related
$T_{\mathrm{gas}}$
$\theta_{\mathrm{air}}$
$\theta_{\mathrm{gas}}$
Used in
$\alpha_{\mathrm{gas}}$
$h_{\mathrm{tr}}$
$\mathrm{Pr}_{\mathrm{gas}}$
$T_{\mathrm{conv_{\mathrm{ce}}}}$
Choices
GasPressure0°C15°C25°C240 K300 K320 K340 K360 K400 K
Air1 bar0.024360.0254990.026247
N21 bar0.0240010.0251080.0258350.021480.025970.027390.028790.030150.03281
N210 bar0.02190.026290.03304
SF61 bar0.0116270.0127010.013412
CO21 bar0.0146750.0158440.0166430.012240.016790.018420.020090.021770.02514
CO210 bar0.012940.017250.018840.020470.022120.02546
CO1 bar0.024740.025790.026478
O21 bar0.024350.025550.02634
H21 bar0.172580.180050.18488
NH31 bar0.0229160.0240730.024934
SO21 bar0.0084340.0090920.00954
He1 bar0.14620.151690.15531
Ar1 bar0.0164830.0172450.017746
Kr1 bar0.0086520.0090820.009363
Xe1 bar0.0051070.0053650.005535