This dataset is the work of Oliver Gould and Tuomas V.I. Tenkanen. It collects the numerical data from the paper "Perturbative effective field theory expansions for cosmological phase transitions" (2023). It primarily contains data from perturbative calculations of the thermal evolution of the real-triplet extended Standard Model at two benchmark parameter points. In addition, for comparison to the perturbative results, we have included data of the scalar quadratic condensates as a function of temperature from the lattice Monte-Carlo simulations of Lauri Niemi, Michael J. Ramsey-Musolf, Tuomas V.I. Tenkanen and David J. Weir, from the paper "Thermodynamics of a Two-Step Electroweak Phase Transition" (2020). We thank the authors for granting permission to reproduce this data here. Everything is contained within the archive file triplet_two_step_data.tar.gz, a tarball compressed with Gzip. For further details and for the context of this dataset, see the above papers. Details of the conventions used in the dataset can be found in the accompanying README.md file.