Extrudate swell is an important viscoelastic feature of polymer melt processing. Experimental work with linear polymers has identified extrudate swell to depend strongly on average molar mass and molar mass distribution. Unfortunately there was no method identified to distinguish the relative effects of average mass and polydispersity. This paper revisits previously published experimental data on high-density polyethylenes and proposes a model to understand the coupled effect of these two molecular variables. The model connects findings from double reptation models via the recoverable compliance to extrudate swell. The reported results provide support to the model and lead to a better understanding of the important role of high-mass fractions in polydisperse polymers. (C) 2007 Elsevier B.V. All rights reserved.