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 DSC. However, for investigation of fast technical processes the heating and cooling rates are not sufficient. We introduce a novel analytical method called SECA (stability estimate by crystallization analysis) for short time stability based on fast scanning calorimetry (FSC). This method analyses the change in the crystallization kinetics due to thermal stress. FSC enables the extrapolation to fast heating rates because the time constants of the instruments are in the millisecond range. The measurements can be performed at heating and cooling rates in the order of several thousand K/s. At such scanning rates the degradation can be prevented. SECA is used for analyzing polyamides, poly(ether etherketone) (PEEK) and polymer materials developed for selective laser sintering (SLS). 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.