The relief in ultrathin sections is interpreted as one of the reasons for the image contrast observed in low-voltage transmission electron microscopy. In order to clarify this, processes taking place in the course of ultrathin sectioning were monitored using a polymeric material composed of hard matrix and soft particles (high-impact polystyrene). Volume changes leading to a surface relief were observed both on cut surfaces and in ultrathin sections. (C) 2001 Elsevier Science Ltd. All rights reserved.