A dry-air-surface heat exchanger is provided for use in a liquid cooling tower, and includes a plurality of preformed, shape-retaining heat transfer members of relatively thin synthetic resin sheet material. Each member presents a pair of upright, side-by-side panels that are preferably folded together about a vertical axis to present inward-facing wet-transfer surfaces adapted to transfer heat between the fluid and the member, and an outward-facing dry-transfer surface adapted to transfer heat between the member and air. The folded member is configured to present a series of tortuous liquid flow paths between the panels extending between the upper and lower edges, and the side edges are secured together in substantially fluid tight sealing engagement. A plurality of the folded members are provided in a pack, and a diffuser is positioned adjacent to the upper edges of the folded members for receiving hot liquid and directing the hot liquid between the panels of each member. The diffuser seats against the upper edges to substantially uniformly distribute the fluid to be cooled into the fluid passages while keeping the air passages therebetween free of fluid. The ratio of the total vertical, cross-sectional area of the liquid passages through the heat transfer members with respect to the total vertical, cross-sectional area of the air passages between the heat transfer members is from about 0.67 to about 1.5.