The data comprise the composition-dependent ice-active fractions (f_ice) in the ammonium sulfate-letovicite-ammonium bisulfate (AS-LET-AHS) system, measured with the AIDA cloud chamber and the two continuous flow diffusion chambers (CDFCs) INKA and mINKA. The provided zip-file contains the two directories "Fig6" and "Fig7" and the additional text file “info.txt”, which explains the contents of the directories and the syntax of the file names. All data tables can be opened in standard text editors or imported in spreadsheet programs like Microsoft Excel. The data are separated by tabs as a delimiter.