Polar Radiant Energy in the Far InfraRed Experiment (PREFIRE) Satellite 1 Cloud Mask (PREFIRE_SAT1_2B-MSK) contains a binary clear/cloud indicator and probabilities derived from data collected by the PREFIRE Thermal Infrared Spectrometer (TIRS-PREFIRE) aboard PREFIRE-SAT1. Dual CubeSats each carry a PREFIRE Thermal Infrared Spectrometer (TIRS-PREFIRE), a push broom spectrometer with 63 channels measuring mid- and far-infrared (FIR) radiation from approximately 5 to 53 µm. Most polar emissions are in the FIR but have not been measured on a large scale. PREFIRE aims to fill knowledge gaps in the global energy budget by more accurately characterizing polar emissions. This information will then be assimilated into global circulation and other models to predict future conditions more accurately. PREFIRE_SAT1_2B-MSK is derived from mid-infrared and far-infrared measurements collected globally by TIRS-PREFIRE aboard PREFIRE-SAT1 using a Machine Learning technique. Specifically, inputs are PREFIRE Spectral Radiance (PREFIRE_SAT1_1B-RAD) from PREFIRE Satellite 1 (PREFIRE_SAT1_2B-RAD) and PREFIRE Auxiliary Meteorology Data created for PREFIRE Satellite 1 (PREFIRE_SAT1_AUX-MET). PREFIRE_SAT1_2B-MSK is used to identify cloudy and clear scenes in TIRS-PREFIRE data, which supports the production of other Level 2 PREFIRE products. These include variables such as top of atmosphere spectral flux, surface spectral emissivity, and atmospheric properties such as temperature and water vapor profiles. Science data retrieval started July 24, 2024 and is ongoing. Geographic coverage is global, with the greatest concentration of data in the polar regions. Within the orbital swath there are eight distinct tracks of data associated with the eight separate spatial scenes for each PREFIRE-TIRS. At the beginning of the mission, the approximate scene footprint sizes were 11.8 km x 34.8 km (cross-track x along-track), with gaps between each scene of approximately 24.2 km. The entire swath was ~264 km across. Note that the scene footprint and swath sizes quoted here are for the orbit altitude soon after launch. However, the footprint size will slowly become smaller as the orbit altitude decreases with time. This data has a temporal resolution of 0.707 seconds and is available in netCDF-4. The cloud identification data for the sister instrument aboard PREFIRE-SAT2 can be found in the PREFIRE_SAT2_2B-MSK collection.