The insulation efficiency of rigid polyurethane foams can be improved by in
creasing the cell isotropy of the polymer matrix and decreasing the heat ra
diation effect. The influence of the foam growth direction on the thermal p
roperties of foams may be considerable, as shown by measurement of the ther
mal diffusivity. The modified Angstrom method was used for the measurement
of the thermal diffusivity D of rigid polyurethane foams. The influence of
sample preparation and the measurement conditions on the D-values were stud
ied. It was found that to compare the insulation properties of polyurethane
foams, the measurement conditions must be carefully chosen. The ability to
use small-dimension samples makes this method very useful for the local me
asurement of the anisotropy of thermal properties of insulation foams.