Apparatus for applying thermotherapy to a part of the human or animal body comprising an applicator (610) having a flexible enclosure in which thermal energy transfer fluid can circulate, a connector for connecting the applicator to a control system, an interface layer for providing a thermally conductive interface between the flexible enclosure and a treatment site and, an electrically conductive supporting layer for supporting the interface layer and capable of being energised by an electrical signal from the control system to improve the thermal conductivity of the interface layer. The apparatus also includes a valve unit (650) for connecting the applicator to a control system, a heat exchanger for cooling a thermal energy transfer fluid and a control system (605) for controlling the application of thermotheraphy. The apparatus permits manipulation and control of the molecules of the interface layer and a thermal energy transfer fluid to improve the thermal energy transfer efficiency between the applicator and a treatment site.
