A retaining element for use with elastic sheet material is disclosed. In one form, the sheet material can be provided as a bag (100) having first and second side walls (102, 104). The retaining element can be in the form of an elastic strip attached to one of the side walls. The retaining strip (120) can comprise a heat-unstable activatable material such that it can be applied to the bag in a deadened condition wherein the strip is set and subsequently heated to transition to an activated condition wherein the retaining element is elasticized to provide an elasticized article which can have a shirred appearance. The retaining element can have various configurations and can be activated by various methods.