Since the grid design was identified as the most efficient insert design, two additional modifications of this design were developed and investigated: i) the round grid design and ii) the double grid design. Both designs were developed to improve printability and to increase the absolute surface area for photocatalysis. Since only optically accessible areas can be photocatalytically active, the fraction of surface areas exposing the TiO2-PP composite to the light was increased. With the round grid design, the rectangular arrangement of the struts forming rectangular holes was changed to round holes with a diameter of 3 mm, primarily to improve printability. The nominal irradiated area was only increased slightly to maintain comparability with the normal grid design (see Table ). Alternatively, the double grid design uses rectangular holes but with an increased mesh width, to further improve printability. In addition to this, a second grid is placed below the first grid and rotated such that holes of the first grid layer were covered mostly by the material filled areas of the second layer, increasing the irradiated area to 9.53 cm². A complete overlay of the grids was intentionally avoided to minimize the pressure drop caused by the redirection of the liquid. By using either method, printing errors could be decreased and print quality could be enhanced.