Abstract: A partially crystalline copolyamide formed from an aromatic carboxylic acid that is terephthalic acid or a mixture of terephthalic acid and isophthalic acid containing less than 40% of isophthalic acid, and an aliphatic diamine that is a mixture of hexamethylene diamine and 2-methyl pentamethylene diamine. The aliphatic diamine is at least 40%, molar basis, of hexamethylene diamine and the amount of isophthalic acid plus 2-methyl pentamethylene diamine is in the range of 15-35%, molar basis, of the total amount of aromatic carboxylic acid and aliphatic diamine. The copolyamides have a melting point of 280.degree.-330.degree. C. The copolyamide preferably has a heat of fusion of greater than 17 J/g. The copolyamide may be moulded into articles, spun into fibres or formed into films, and used in a wide variety of end-uses especially where high temperature properties are required.