Commercial poly-3-hexylthiophene was used to create thin films, which were analyzed to determine density, the dependence of the optical absorption on film thickness and the effects of impurities on the optical properties of the polymer. Rutherford backscattering spectroscopy (RBS) demonstrated Zn and Br impurities in the films, which could be removed with methanol extraction. These impurities affect the optical properties of the polymer. Film thicknesses were measured using atomic force microscopy, and in combination with the RBS data, the density of the polymer film was ascertained to be 1.33 +/- 0.07 g/cm(3). The dependence of the polymer absorbance on the film thickness is well modeled by the linear function T = (136.8 +/-2.4) x (A((lambdamax))) + (6.9 +/- 2.0), where T is the film thickness and A((lambdamax)) is the absorbance maximum.