Polyamide vs Polyester: Guide to Material Selection & Uses

Polyamide and Polyester are two major families of synthetic polymers, both of immense industrial importance but with distinct chemical structures and resulting property profiles. Their fundamental difference lies in the functional group of their polymer backbone: Polyamides (Nylon) feature amide groups (-NH-CO-), while Polyesters (like PET, PBT) feature ester groups (-O-CO-). This structural distinction leads to several key performance differences. Regarding mechanical properties, polyamides generally offer superior toughness, impact resistance, and abrasion resistance. Polyesters, particularly when reinforced, often exhibit higher stiffness and tensile strength. A critical differentiator is moisture behavior: polyamides are highly hygroscopic, absorbing significant amounts of water which plasticizes the material, increasing toughness but reducing stiffness and dimensional stability. Polyesters, in contrast, are much more hydrophobic, with very low moisture absorption, resulting in excellent dimensional stability in humid environments. Thermally, polyamides like PA66 have a higher melting point than PBT, but polyesters typically have a higher Heat Deflection Temperature (HDT) in their glass-filled forms. Chemically, polyesters generally offer better resistance to a broader range of chemicals, including strong acids, while polyamides have excellent resistance to oils and hydrocarbons. In terms of cost, commodity polyesters like PET are often less expensive than standard polyamides, though engineering-grade versions can be comparable. The choice between them is application-driven: Polyamide is preferred for tough, wear-resistant parts that can tolerate some dimensional change (gears, bearings), while Polyester is chosen for dimensionally stable, stiff components in humid or chemically challenging environments (electrical connectors, automotive housings).