This study investigates the potential use of waste photopolymer printing matrices as fillers in polymeric materials. Ground printing matrices were incorporated into polypropylene at concentrations of 10, 20, and 30 wt.% and evaluated for selected physical, mechanical, and thermal properties. Spectroscopic analysis indicated that the matrices consist of polyesters and styrene–butadiene copolymer. The resulting composites maintained low density (<1 g/cm³), compared to 0.896 g/cm³ for neat polypropylene. Contrary to most literature reports, the addition of ground printing matrices led to a reduction in mechanical performance. At the highest filler content, tensile strength decreased by 50% (from 22.7 to 10.9 MPa), Young’s modulus by 33% (from 1290 to 825 MPa), and flexural strength by 38% (from 37 to 23 MPa). The most pronounced decrease was observed in impact strength, which dropped by 67% to 17 kJ/m². Thermal properties were affected to a lesser extent. The filler slightly reduced the crystallization temperature but simultaneously improved the thermal stability of the composites, with higher filler loading yielding greater enhancement. The observed reduction in material properties is primarily attributed to poor matrix–filler adhesion, representing a key challenge for further development. Nevertheless, the performance remains acceptable for the intended applications. Overall, the study successfully demonstrates the feasibility of using post-production label waste as a polymer filler.