An assembly for packaging a product includes a blank of sheet material having an interior surface and an opposing exterior surface. The blank forms a carton having a top, a bottom and a plurality of side panels. Each side panel extends between the top and the bottom. A first side panel is movable between a first position and a second position. The first movable side panel is initially biased in the first position. A heat-shrink patch is applied to the interior surface and connected to at least a portion of the first movable side panel. The heat-shrink patch is shrinkable to urge the first movable side panel to the second position.