A serpentine fin for assembly between tubes in a heat exchanger core, and a method of making same from a metal strip. The strip edges have a hem comprising a double thickness of the strip material extending inward from the edge. The metal strip has folds extending across the strip width such that the strip forms a serpentine shape, with the folds being adapted to contact the tubes in the heat exchanger core. Multiple rows of split louvers are disposed between adjacent folds. Each row of split louvers comprises louvers having openings extending in the direction of the strip length and formed in a pair of adjacent, spaced louver banks. Ribs are disposed parallel to the louver openings adjacent the strip edges and in at least one center portion of the strip between the strip edges, and extend across the pair of louver banks.