Abstract: A material for forming a hollow-molded body, which comprises a polyamide comprising hexamethylene isophthalamide units as the main recurring units. A hollow-molded body having an excellent gas barrier property can be obtained by using this polyamide molding material alone or in combination with polyethylene terephthalate.

Abstract: A process for producing a thin-walled cylindrical body of an aromatic polyester, which comprises(A) heating a continuous thick-walled tubular body of an aromatic polyester by introducing it continuously into a heating zone while feeding a pressure fluid into the thick-walled tubular body,(B) expanding the heated thick-walled tubular body into a cylindrical form, and(C) continuously stretching and taking up the resulting cylindrical expanded body, while at least forming a fold-free portion in the expanded body in its longitudinal direction; and a thin-walled cylindrical body of an aromatic polyester characterized by a specific intrinsic viscosity, density, wall thickness, surface roughness (CLA), and difference of its refractive indices in the circumferential direction and in a direction perpendicular to the circumferential direction, and substantial freedom from folded marks which cannot be removed at a temperature of 80.degree. C.