Abstract: The heat exchange structure made by the method of the present invention comprises a plurality of sheets, desirably thin film plastic, bonded to one another to form the unitized structure. Alternate first pairs of sheets are bonded one to another along a first set of longitudinally extending bond lines positioned at first transverse locations along the width dimensions of the sheets. There is a second set of pairs of alternately spaced sheets (made up of adjacent sheets of adjoining first pairs of sheets) which are bonded one to another along a second set of longitudinally extending bond lines positioned transversely intermittently with respect to the first set of longitudinal bond lines. In the method of the present invention, the sheets are arranged in vertically stacked relationship. One set of bonding bars is positioned between sets of adjacent intermediate pairs of sheets at the locations where the first set of longitudinally extending bond lines are to be formed.