Abstract: A method for substantially reducing the variance in results obtained in pull tests on reclosable plastic bags, wherein the forces needed to open the bags from within and from without are measured and compared, by controlling the attachment point of the bag wall to the base of the zipper profile requires the use of selectively placed preferential seal areas. These seal areas are provided by disposing an interlayer between each profile and its respective bag wall. The interlayers include a strip of material having a lower melting point than those of the profiles and the bag walls and having a preselected width greater than any possible lateral displacement, or "float", of the profiles that may occur in the sealing apparatus. Where the strip does not take up the entire width of the interlayer, it has a preselected, constant width and runs parallel to the zipper profiles. The lower melting point of the material of the strip, and the width of the strip, ensure that the seal location on the profiles remains fixed.