The thermal short time stability is relevant for fast heating processing techniques like fused filament fabrication, selective laser sintering or polymer welding. Also the application of polymeric materials with temporary stress at high temperatures requires knowledge of the short term stability at high temperatures. Thermogravimetric analysis (TGA) is a standard technique to measure the thermal stability. This technique has two drawbacks: • The decomposition at high temperatures does not necessarily contain the same reaction steps as measured by TGA. • TGA is not sensitive for degradation steps which are not related to mass loss. However, such reactions can significantly influence the properties of polymeric materials. It is shown on differently stressed polymers that the crystallization behavior changes sensitively with molecular modifications due to the stresses. The modification in the crystallization behavior due to thermal stress can be studied by fast scanning calorimetry (FSC). The change of the crystallization kinetics due to thermal stress is analyzed. From the measured curve a stability parameter can be derived which characterized the thermal degradation. The stability of polyamides and polymer materials developed for selective laser sintering (SLS)is analyzed for fast heating processes. The results show a remarkable discrepancy to the TGA results and the high sensitivity of the change of the crystallization behavior for the early steps of decomposition reaction.