To obtain a daylighting board which is selectively inhibited from transmitting light in the region of heat rays and has the strengths of a reinforced plastics by incorporating specific mica particles and glass fibers into a light-transmitting plastic substrate.

This plastic board 1A contains glass fibers 4 and mica particles 3 of which 40-60% of the surfaces are covered with titanium oxide and the thicknesses are adjusted to 60-160nm. The mica particle is obtd. by forming a titanium oxide layer on the surface of a mica flake by vapor deposition, etc. This board may be one wherein the mica particles are homogeneously dispersed or one wherein they are localized near one surface, and the latter one utilizes the heat-ray-intercepting capability of the particles to the full, thus providing the same heat-ray-intercepting effect with a smaller amt. of the particles.