PURPOSE: A cheap light-transmitting heat-insulating material with excellent heat insulating property and selective transmittance, obtd. by incorporating a light-transmitting inorg. powder having a selectively transmitting semiconductor film on its surface in a synthetic resin.

CONSTITUTION: A synthetic resin is compounded with pref. 0.05W20wt% light- transmitting inorganic powder having a selectively transmitting semiconductor film on its surface. Said inorganic powder is pref. one excellent in heat resistance because of possibility of chemical treatment in the formation of the semiconductor film, and lamellar on of high aspect ratio such as powdered silica, mica or galss flake is pref. because of increased effect of selective transmittance when flatly arranged. A semiconductor doped with an oxide such as indium oxide or titanium oxide, a halide such as copper iodide, etc. is used as said selectively transmitting semiconductor.