In laser transmission welding of polymers, additives and colorants could influence the welding result. In this work, polypropylene and polycarbonate probes colored with titanium dioxide (TiO2) pigments of various concentrations are investigated. The probes are produced using an extrusion process to obtain a homogeneous distribution of colorants. The TiO2 pigments change the optical properties of the polymers considerably. The measured reflectance increases with increasing pigment load while the transmittance decreases. From the measured data of transmittance, reflectance, and collimated transmittance, the scattering, the absorption coefficient, and the anisotropy factors are calculated. It is shown that the scattering coefficient at 1530 nm (laser) wavelength is smaller than for 968 nm, while the absorption coefficient is negligible for both wavelengths. Scattering coefficient and anisotropy factor are used to simulate the propagation of the laser radiation in the polymers. The influence of the scattering process on the beam propagation is represented by the change of the power density distribution. It is shown that the maximum intensity of the distribution is reduced more than the transmittance with increasing pigment concentration. The effect is higher for 968 than for 1530 nm wavelength making the larger wavelength more favorable for transmission welding. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40073.