Through textile recycling, resources can be saved, and landfilling can be avoided. However, determined input streams are needed for high-quality recycling processes. The aim of this study is to investigate the detection, prediction and sorting of polyester-containing textile waste using near-infrared spectroscopy. In experimental trials, polyester-containing textiles with different fibre blends are scanned, and the spectra are recorded. The results are evaluated in a linear regression model and transferred to an industrial-scale sorting plant. Due to the different peaks in the spectra of the investigated fibre types and a visible correlation of the absorption intensity between the blend ratios, the use of NIR spectroscopy is very promising for application in the sorting of polyester-containing textiles.