<p>This study explores the impact of 1-octadecanol-functionalized carbon nanotubes (cCNTs) on the rheological, mechanical, morphological, and physical properties of ethylene-propylene-diene monomer/styrene-butadiene rubber (EPDM/SBR) nanocomposites. Key performance indicators assessed include abrasion and swelling resistance, compression set, and crosslink density. Field emission scanning electron microscopy (FESEM) of fractured tensile specimens confirmed uniform dispersion of cCNTs within the rubber matrix. Rheometric analysis using an oscillating disc rheometer showed that increasing cCNT content led to higher minimum torque, maximum torque, delta torque, and cure rate index, while scorch time and optimum cure time decreased. Mechanical testing revealed that tensile strength and stress at 100% elongation improved with cCNT loading up to 6 phr (parts per hundred rubber), with tensile strength increasing by 206% compared to the unfilled base compound, before declining at higher concentrations. Tear strength, hardness (measured with a durometer), DIN abrasion resistance, swelling resistance, compression set (ASTM D395), and crosslink density (calculated using the Flory–Rehner equation) also improved with rising cCNT content. However, elongation at break decreased due to constrained chain mobility, and rebound resilience, assessed using a resilience tester, also declined with higher filler levels. These findings highlight a balance between enhanced polymer–filler interactions and increased filler–filler networking, both of which critically influence the final performance of EPDM/SBR nanocomposites.</p>