A sealing element for a heat exchanger is defined by an elongate main body. An aspect ratio of the main body is greater than 1:1, wherein a height of the main body is greater than a width of the main body. The sealing element includes a plurality of enlarged portions spaced at predetermined intervals along a length of the main body. The enlarged portions have a width greater than the width of the main body, and are laterally offset inwardly with respect to the main body. The sealing element further includes a plurality of lugs protruding laterally from the main body. First pairs of the lugs are alternatingly arranged with the enlarged portions of the sealing element. Second pairs of the lugs are spaced along ends of the sealing element. Single ones of the lugs also protrude laterally outwardly from the enlarged portions.