The apparent temperature of nonisothermal sheets with a wavelength dependent absorption coefficient was investigated. A polypropylene sheet with a parabolic temperature distribution across its thickness was used as an illustration of apparent temperature calculations. It was found that the variation of the apparent temperature of polypropylene with thickness was different from that of gray media (with absorption coefficient independent of wave length). This difference was attributed to the effect of thickness on the spectral distribution of the radiation emitted by the sheet.