The equation we have used for thermal conductivity is: K = (0.813/d)*(1-(0.0003*(t-32)))
d is the specific gravity at 60F/60F
t is the temperature in F
K is the thermal conductivity (BTU-in)/(hour-ft2-F)This information comes from page 870 of Asphalts and Allied Substances, 4th Edition, by Herbert Abraham (published in 1938).