The invention involves a flat fin heat exchanger configuration 10 with a plurality of louvers 26 that are raised above the plane of the fin 16 between adjacent tube holes 19, 20 that receive tubes 14. Various alternative patterns of louvers enhance the heat transfer characteristics of the fin, and allow for the use of thinner materials to lower cost without diminishing performance. The exterior fin surface redirects air flow from the leading edge to the trailing edge of the fin. This effect directs the air flow over and in between the interrupted surfaces, thus breaking up air boundary layer around the fin. The louvers of the fin are oriented relative to the air flow in such a manner that each louver in effect creates another leading edge, thus contributing to a higher heat transfer coefficient.