In selective laser sintering (SLS) polyamide 12 powder (PA12) is predominantly used for sintering components. Often, after the sintering process approximately 70 % of powder, which has not been sintered, remain. The properties of this used powder have been deteriorated because of the thermal stress during sintering process. Due to the high price of new PA12 powder, the used and aged powder must be recycled by refreshing it with new powder. This powder mixture can then be reused in a next sintering process. However, due to the repeated refreshing process of the aged powder, mixtures are produced whose quality is difficult to define. They differ greatly in their flow properties, which in turn has a negative effect on the component quality. In order to generate a good and reproducible powder quality, the thermal aging behavior of PA12 powder has been examined in detail by the IKT. Based on these results, a recycling process could be developed step by step, by which the thermal aging can be reversed. A chemical agent is added to the aged powder which is able to cleave the long polymer chains of the aged powder at its amide bonds. Depending on the kind of chemical agent used and its concentration, the flow properties of the aged powder can be adjusted selectively, which also makes the quality of the "refreshed" mixtures reproducible. By means of this recycling process, the aged powder can be reused several times. Thereby, it contributes to material and cost efficiency and thus leads to an increased cost effectiveness of selective laser sintering.