Leads (open water and thin ice) were classified in helicopter-borne thermal infrared observations. Lead classification maps, gridded in 1 m resolution, are provided for 35 flights between 02.10.2019 and 23.04.2020 during the MOSAiC expedition in the Arctic ocean. There is one file for every flight, either on a local (MOSAiC central observatory) or regional scale (MOSAiC distributed network). The flights can be identified by two campaign specific IDs (the event-related Device Operation label or Flight ID). The lead classification maps are derived from the surface temperature maps (doi:10.1594/PANGAEA.941017) as described in Thielke et al (in preparation). The 5 m resolution data (based on block averaged surface temperature) are included to provide data with a smaller file size so they are easier accessible and available for the comparison of the effect of different spatial resolutions. The binary lead classification is performed with a temperature threshold. In this data set, in addition to the lead classification maps, also the surface temperature and time-fixed surface temperature maps are included (the same data as included in the temperature maps: doi:10.1594/PANGAEA.941017). This time-fixed surface temperature is necessary to perform the classification and included for direct comparison to the lead classification result. All data are georeferenced, also as relative coordinates to the position of RV Polarstern which allows a Polarstern centered, Lagrangian view on the lead development.