Kapton-H type is an optical plastic with an UV-Vis-NIR spectrum characterized by abrupt absorbance change at a wavelength of ca. 550nm. Such sharp optical discontinuity, known as fundamental absorption edge, has been investigated by the Tauc plot method and a band gap energy (Eg) of (2.22±0.05) eV for an indirect transition model has been found. The Cody plot has been also applied and a slightly lower band gap energy value (i.e., Eg = 2.33±0.05 eV) was found. The Urbach rule applied to the spectrum tail has provided an Urbach energy value (EU) of ca. (185±2) meV, which is a quite high value, fully compatible with the highly disordered structure of this sterically rigid amorphous polymer. Cut-on wavelength (550nm), visible transparency (T% of ca. 80), and other relevant optical characteristics of Kapton-H type have been evaluated too.