Cellulose is found in the walls of plant cells, making it the most common biopolymer in the world. It is mechanically stable, resistant to hydrolysis, and boasts—especially in its nanoscopic state—a large reactive surface area and low density. To realize reinforcement in rubbers, the large and polar cellulose surface must interact with the nonpolar elastomer matrix. The dispersion of hydrophilic fillers is, however, still a major challenge in rubber technology. In this work, commercially available nanofibrillated cellulose (NFC) was incorporated into a nonpolar BIIR via latex mixing. Transmission electron microscopy, tensile testing, swelling, and rheometry were used to characterize the compound properties and the reinforcing potential of NFC. The compounds were compared with the established and highly dispersible standard carbon black N550 with a medium specific surface area. In addition, hybrid filler systems with both particle types were prepared. This yielded well-dispersed nanocomposites of a new kind exhibiting high stiffness, good tensile properties, and reduced material weight.