Abstract: A thermal conditioning unit to thermally condition a substrate in a lithographic apparatus, the thermal conditioning unit including: a thermal conditioning element having a first layer, in use, facing the substrate and including a material having a thermal conductivity of 100 W/mK or more, a second layer and a heat transfer component positioned between the first and second layers; and a stiffening member which is stiffer than the thermal conditioning element and configured to support the thermal conditioning element so as to reduce mechanical deformation thereof, wherein the thermal conditioning element is thermally isolated from the stiffening member.