Copper indium disulfide thin films were deposited by vacuum thermal evaporation method. The interest of this study is focused on the effects of substrate heating conditions on the layer growth and properties. It was found that a longitudinal thermal gradient (LTG), even small, induces drastical changes in optical properties of the layers which behave as a highly absorbing material. Crystallized resistive and highly absorbing as-made layers were studied in comparison with "standard" CuInS2 samples (conductive heating at 250 degrees C). Electrical, structural, and optical analysis showed that the involved prominent property (i.e., opacity) seems to be a volume effect occurring during growth stage and is clearly correlated to LTG conditions. On the other hand, thermal cycling in vacuum in the 293-573 K range did not show any electrical disturbance as exhibited in the "standard" CuInS2 case.