Constitutive equations represent a powerful tool for analysis and description of linear and branched polymer materials (even for polydisperse ones). Predictive/fitting capabilities of three constitutive models (eXtended Pom-Pom, PTT-XPP, and modified Leonov models) were examined using four standard industrial PE materials (two linear and two branched). All the materials were tested in both shear and uniaxial extensional flows (steady and transient)