A preactivation procedure was applied for further experiments to enable the comparison of different catalyst loadings and insert designs. As preactivation procedure a 20 h (𝑡 𝑝𝑟𝑒 ) irradiation with UV light (λ = 365 nm) of the inserts immersed in water was applied. For the actual reactive characterization of the inserts, the preactivation was followed by multiple 4 h periods (𝑡 𝑒𝑥𝑝 ) during which the MB decolorization was conducted with fresh MB solutions. A variation of the TiO2 loading between 𝜔 𝑇𝑖𝑂2 = 0.05 and 0.15 (𝑚 𝑇𝑖𝑂 2 𝑚 𝑃𝑃 -1 ) revealed that a loading of 𝜔 𝑇𝑖𝑂2 = 0.05 is almost inactive, showing not more than 3 % conversion of MB after 76 h of irradiation (see Figure ). Increasing the TiO2 loading to 0.1 or 0.15 resulted in average conversions of about 10 % or 19 % after 76 h, respectively. Some deviations in conversion in the region of 3 % to 5 % can be observed for the different printed inserts, especially for short reactions times. For longer reaction times, the registered conversions only differ slightly. The differences are attributed to differences occurring during the manufacturing of the TiO2-PP filaments and the printing of the inserts. During manufacturing of the filaments, it turned out that maintaining a homogenous distribution of TiO2 in the composite is challenging since TiO2 tends to separate from the PP granulates. Consequently, quality differences of the filament and with this also the printed inserts are to be expected. With increasing reaction time, the accessibility of the TiO2 particles increases and also local inhomogeneities are equalized, eventually leading to comparable activities.