The preparation of functional photopolymer nanocomposites is affected by both the physical and chemical interactions of nanoparticles (NPs) and polymer resin. Some NPs, such as semiconducting metal oxides, may contribute by their photocatalytic behavior and electron transfer, influencing the kinetics of the photopolymerization reaction. This study has investigated the complex effect of titanium dioxide (TiO 2 ) NPs in anatase and rutile form on the conversion, kinetics, and printability of free -radical and cationic photopolymerization resin. Two different polymorphs of TiO 2 NPs ensured identical chemical properties, but different physical effects related to their varying band gap energies and electron transfer efficiency. These parameters were found to be crucial for influencing the photopolymerization kinetics. While rutile showed a more pronounced enhancement of the free -radical photopolymerization ' s conversion and kinetics, cationic photopolymerization was favourably affected only by anatase NPs due to the photosensitization effect. These findings are critical in understanding and designing functional nanocomposite materials processed by vat photopolymerization 3D printing that could find use in optical, medical, or environmental applications.