Microcellular aluminium can be produced by replication in porous material with pores across a wide range of sizes but with otherwise identical structures. Compressive tests reveal a plasticity size effect, with samples showing higher strengths and higher rates of work hardening for smaller pore diameters. This size effect is shown to be dislocational, its main origin being dislocation emission during the composite stage of foam processing. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.