This study was undertaken to compare the exothermic properties of three leading casting materials used in orthopaedics (Delta Lite S, Dynacast Extra and Scotchcast Plus) and to examine the factors Hospital, Bridgend which could influence the maximum temperature produced beneath casts made from them both in the laboratory and under simulated 'in use' conditions. Each bandage was applied with four, five or six turns to a model leg and the temperature beneath the cast was measured at five-second intervals over a 10-minute period. In this test, Dynacast Extra produced a higher temperature than the other products examined, but not sufficient to cause damage if the manufacturer's instructions are followed. The maximum increase in temperature of a standard mass of water, and water uptake during activation were also measured. When the temperatures produced beneath the casts in vivo were measured using a volunteer, no significant differences between the bandages were detected. The authors conclude that the risk of thermal damage during the application of orthopaedic casts can be minimised by careful attention to the manufacturer's guidelines; they also provide additional recommendations for safe usage of the materials.