Three high density polythylenes with widely differing molecular weights have been subjected to a fast fracture process and studied by scanning electron micrography. Two polymers in the low to medium molecular weight range show evidence of substantial melting during facture, in support of some previous work. On the other hand the ultra high molecular weight material seems to deform on a more massive scale without recognisable relics of a melting process. (C) 2004 Elsevier Ltd. All rights reserved.