This document provides details on the files available for download in the data set "In situ thermography of the metal bridge structures fabricated for the 2018 Additive Manufacturing Benchmark Test Series (AM-Bench 2018)." The experiments were performed to support the 2018 AM-Bench1 Class 01 experiments consisting of metal three-dimensional (3D) builds. The modeling community was invited to predict the following: (1) part deflection, (2) residual elastic strains, (3) microstructure, (4) phase fractions, and (5) phase evolution. Details for these proposed challenges and the postprocess measurement results can be found at their respective links on the AM-Bench website.1 This document describes the experiments conducted on a commercial laser powder bed fusion (LPBF) machine and the in situ thermography and explains the resulting measurement data. The purpose of disseminating these data is twofold: (1) to provide layer-wise thermal history data for part-scale model validation and (2) to provide insight into the thermal history responsible for the postprocess distortion, residual strain, and microstructure. Measurements are reported in radiance temperature. The calculation of true temperature for direct comparison with model results requires knowledge of the effective surface emissivity. At this time, the effective emissivity is unknown, but assumptions can be applied based on the literature. The following sections detail the experiment and measurement setup, describe the data files, and provide equations to enable the calculation of true temperature from the measured radiant temperature. © 2020 National Institute of Standards and Technology. All rights reserved.