AbstractFor molten polymers, each theological property provides a different basis for comparison and characterization. This point is illustrated by reference to the results of an extensive testing program involving a series of four commercial blow molding resins, each produced by a different Canadian manufacturer. Three high density polyethylenes were studied at 170°C, while a polypropylene was studied at 190°C. Properties measured included viscosity, first normal stress difference, dynamic viscosity, storage modulus, extrudate swell as a function of time and shear rate, and stress growth functions for both shear and uniaxial elongatio