The improvement of the processing condition for selective laser sintering (SLS) is from fundamental importance for the mechanical, optical and surface properties of the products. This includes the behavior of the used polymer powder, the situation in the building chamber and the conditions during the sintering process. Commonly the determination of the processing parameters is based on conventional DSC and TGA measurements. This is however problematic because the experimental conditions of these techniques (sample size, heating and cooling rate) do not fit the process conditions. The stable sintering region is characterized by the melting temperature on one side and the decomposition onset on the other side. The dependence of both properties on the heating conditions during the sintering process is discussed and approaches to measure these properties at processing relevant conditions are proposed. It is shown how the melting and decomposition behavior of powder partials can be measured at processing relevant heating rates of several thousand Kelvin per second using Flash DSC with MEMS based chip sensor. The limits of the stable sintering region determined by this technique differ significantly from the data derived from the conventional DSC and TGA techniques. Investigations are carried out on different materials developed for SLS like polyamides, thermoplastic elastomers and poly(ether etherketone).