Abstract: The closure strip having a pair of longitudinal side walls with undulating top edges configured to mate with the corrugations of corrugated sheet material. The side walls are interconnected by a plurality of support ribs. The side walls are also angled outward toward the bottom edges. A hollow nesting volume is formed between the side and below the support ribs in the region of each of the undulation peaks of the closure strip. This configuration allows successive closure strips to be nested one into another by inserting the undulation peaks of one closure strip into the hollow nesting volume under corresponding undulation peaks in another closure strip.