Heat exchange apparatus comprises a plurality of thermally conductive, moisture impervious sheets. Each sheet comprises a plurality of corrugations. The plurality of sheets are disposed in a stack such that each alternate sheet has its corrugations affixed to and disposed at an angle to the corrugations of an adjacent sheet to provide a plurality of separate flow pathways. The plurality of separate flow pathways comprises first predetermined pathways and second predetermined pathways. The stack of sheets have first end portions disposed to provide a first inlets and a first outlets for the first predetermined pathways and second end portions to provide second inlets and second outlets for the second predetermined pathways. The corrugations forming the second predetermined pathways comprise a wettable surface. The first predetermined pathways are adapted for a first fluid flow and the second predetermined pathways are adapted for a countercurrent second fluid flow.