This paper presents an experimental study to determine the optimal parameters for recycling PET plastic bottles into filaments for 3D printing. The tensile strength of the filament used in 3D printing is investigated. When recycling waste plastic bottles into filaments for use as input material in 3D printing, the key parameters affecting filament quality are temperature (T), mold length (L), and plastic fiber spinning speed (V). In this paper, the author applies the Taguchi experimental design to evaluate the impact of each parameter on filament quality. The results indicate that temperature and plastic fiber spinning speed have the greatest influence on the tensile strength of the plastic filament. The experimental findings also confirm the validity of the analysis conducted in the study. The results of this paper can serve as a reference for recycling waste plastic bottles into 3D printing filaments used for printing models, decorative products, toys, and other similar items.