Nylon-66 (PA66) is an advanced polyamide engineering plastic, synthesized from hexamethylenediamine and adipic acid. It is known for its exceptional strength, rigidity, and heat resistance, outperforming Nylon-6 in demanding applications. With a density of about 1.13–1.15 g/cm³ and a high melting point of 255–265°C, PA66 exhibits excellent thermal stability, making it suitable for high-temperature environments. It has superior wear resistance, low friction, and high tensile strength (80–95 MPa), ensuring reliable performance in automotive, aerospace, and industrial machinery. Its resistance to fuels, oils, and greases further enhances its utility in engine compartments and mechanical parts. Nylon-66 fibers are also extensively used in textiles, carpets, and tire cords due to their toughness and resilience. Although it absorbs moisture, which may influence dimensional accuracy, it retains excellent mechanical properties under varying conditions. PA66 is typically processed by injection molding, extrusion, and spinning. While it is non-biodegradable, it is recyclable, contributing to circular economy efforts. Its higher cost compared to PA6 is justified by superior strength, durability, and temperature tolerance, making PA66 a premium engineering plastic for critical, high-performance applications across industries.