First part of the ExTraS program (an Experimentation program on Traces of Soot) was conducted in order to better understand the processes of fixation, recording and preservation of combustion products in speleothems and thin parietal carbonated crusts that form at cave entrances and on rock-shelters walls and vault. Among the numerous results, we found that soot has different properties depending on the fuels used and the combustion temperature. We wanted to better define the source of these differences (in color, texture, etc.). Therefore we designed a new step of the ExTraS program, in the laboratory, to produce soot in a controlled environment. We will present here the protocol used to unravel the two factors that can modify the soot structure (documented in Raman microspectroscopy): the combustion temperature and the fuel used. We will also present the results of this new experimental phase, which contributes to a better understanding of what the soot Raman signal indicates.