In this paper, we analyze the impact of wavelength- dependent physical impairments, specifically the optical fiber attenuation coefficient (α) and the optical amplifiers noise figure (NF), considering S, C and L bands in a multiband elastic optical network. The calls blocking probability and the distribution of modulation formats among the network accepted calls were used as evaluation metrics. The results obtained for the use of G-652.A optical fiber show that using α and NF with fixed values underestimates the most realistic scenario (α and NF dependent on wavelength). For the use of G-652.D optical fiber, it was possible to obtain a reduction of approximately 63.41% for S band, 95.60% for C band and 98.84% for L band, in terms of calls blocking probability, when the most realistic scenario was compared with the scenario most used in the literature (α and NF with fixed values). In addition, it was verified that, with the most realistic scenario, it was possible to obtain the distribution of more efficient modulation formats using the G-652.D optical fiber with C band.