The obtained TGA curves have a characteristic course for this type of polymers . The absence of significant mass loss in the temperature range 25-150°C indicates that the materials contain negligible moisture. Another notable observation in the context of this study is that composites with corresponding filler content exhibit very similar R600ºC parameter values. Considering that both polymers degrade almost completely (approximately 100 %) at 600 °C and that the ceramic fillers, which were additionally dried before the process, are thermally stable at this temperature, the R600ºC parameter can be approximately correlated with the filler content in the composite. This observation supports the conclusion that the assumed compositions of the composites accurately reflect reality, ensuring the reliability of comparative analyses between materials with the same filler content. In terms of thermal stability, for both PLA and PCL there is a visible relationship indicating a slight decrease in the thermal stability parameters of the materials as a result of the addition of filler. This effect can be attributed to the fact that the HAp particles were neither modified nor supplemented with additives to form covalent bonds between the polymer and the filler. Published scientific studies suggest that the addition of compounds like sodium dodecyl sulphonate (SDS) can promote the formation of such bonds, thereby enhancing thermal stability . An important aspect discussed in the referenced study is that poor dispersion of HAp particles within the matrix can lead to reduced thermal stability. This phenomenon is evident in Figure , where at 4 0% filler content, the matrix becomes saturated with ceramics to such an extent that T5%, T10% and TDTG parameters decrease. What is also worth noting -these parameters are higher for composites with nHAp than with µHAp. Furthermore, the TGA analysis indirectly supports the observation of weaker interactions between PCL and HAp compared to those between PLA and HAp as discussed in section 3.1. The decreases in the individual temperature parameters listed in Table are significantly greater for the PCL-based composites. For example, the TDTG parameter for the PCL/20µHAp sample is 406.3 °C (a 2.3% decrease compared to pure PCL), whereas for PLA/20µHAp it is 364.6 °C (a 0.3% decrease compared to pure PLA). However, in all cases the differences in the parameters discussed are negligible, not exceeding 3% in the most extreme cases. To maintain consistency with other analytical techniques (SEM, TGA, tensile test), the samples for DSC measurements were taken from the measuring section of the tensile test specimens, as in the previous cases. Figure shows the thermograms recorded during the first heating cycle (a, b) and cooling cycle (c, d). The thermogram for the second heating cycle is given in the Supplementary Information (Figure ). Quantitative results for the first two cycles are presented in Table , while those for the second heating cycle are presented in Table . Analysing the 1 st heating curves for PLA-based materials, it can be seen that they generally follow a similar course, which is characteristic of PLA . Three main phase transitions are observable: 1) an inflection in the curve within the range of approximately 40-60 °C, indicating the glass transition; 2) a broad exothermic peak extending from the glass transition to melting, corresponding to the cold crystallization of the polymer; and 3) an endothermic peak associated with the melting of the crystalline fraction of PLA.