A generally planar, conformable evaporative structure, particularly for incorporation in a garment or an item of personal protective equipment as part of a system to cool the wearer's body, includes an envelope of substantially impermeable, flexible material containing: a layer of flexible wick material disposed adjacent to a major face of the envelope and adapted to hold a working fluid in liquid phase for evaporation by heat conducted through the envelope; a layer of flexible, breathable fabric in parallel with the layer of wick material; and an array of flexible ribs such as open helical coils within the layer of breathable fabric adapted to maintain pathways for the flow of working fluid in vapor phase towards a condensation zone.