Liquid radiation curable compositions are disclosed which are suitable for hybrid (i.e. cationic and free-radical) polymerization when processed via additive fabrication equipment utilizing sources of actinic radiation with peak spectral intensities in the UV/vis region. According to one aspect, the compositions possess a first photoinitiator that is an iodonium salt of a non-fluorinated borate anion. According to another aspect, the composition is substantially devoid of a Norrish Type I and/or Type II photoinitiator. Also disclosed are methods of creating three-dimensional parts via additive fabrication processes utilizing sources of actinic radiation with peak spectral intensities in the UV/vis region employing liquid radiation curable compositions suitable for hybrid polymerization, and the parts cured therefrom.