The annealing of mats of aggregated polyethylene crystals was described in a previous paper. The change in properties with increasing annealing temperature was interpreted in terms of two mechanisms, each dominant over a particular temperature range. In a somewhat different sense bulk-crystallized polymer is also an aggregate of crystalline entities bound together, and a comparative study of the behaviour of a selected sample was therefore made. The results, whilst numerically different from those found for mats, confirm that the study of crystal aggregates can provide a key to the understanding of bulk-crystallized polymer in terms of microstructure.