Abstract: A random copolyester is described, comprising recurring moieties represented by formula (I), (II), and (III), and having an intrinsic viscosity of not less than 0.5, wherein said recurring moieties of formulae (I) and (II) are existing substantially in equimolar amount and recurring moieties of formulae (I) and (III) are present in a molar ratio of from 95/5 to 5/95 ##STR1## wherein Ar.sub.1 represents a trivalent aromatic group and Ar.sub.2 represents a divalent aromatic group. In formulae (I), (II), and (III), aromatic rings may be substituted with an alkyl group or an alkoxy group having from 1 to 20 carbon atoms, an aryl group or aryloxy group having from 6 to 20 carbon atoms, or a halogen atom. The copolyester obtained is excellent in heat resistance and flame retardance.

Abstract: The present invention relates to a denier-mixed composite yarn containing 20 weight percent or more coarse filaments whose single filament fineness is 3 deniers or more and 5 weight percent or more fine filaments whose single filament fineness is 1.5 denier or less. Part or all of the coarse filaments are of non-circular cross-section, the stress of the composite yarn at 10% elongation is 2.5 g/d or less, and the composite yarn has a particular distribution of elongation. According to such denier-mixed composite yarn, superior dry feel fullness and softness can be imparted to woven and knit fabrics.