A bag comprising a front panel and back panel sealed at a base of the bag and two sides extending from the base to define a containment region, the bag being open or openable at an opening region opposite the base and where a multi-panel assembly is provided comprised of said front panel and back panel, at least one side being of a gusset formation, a first closure panel comprising a closure element for cooperating with a closure element associated with the back panel to provide an openable and re-closable closure of the opening region, and a non-bonding zone at which the back panel and the first closure panel are prevented from bonding to each other under an application of heat and pressure, the non-bonding zone being located along the length of the openable and re-closable closure, and more distal of the base of the bag than the openable and re-closable closure, wherein in a first mode the first closure panel is associated with the back panel, and the containment region is accessible through a first mode opening the perimeter of which is defined by the front panel and back panel and two sides, and wherein in a second mode, following an application of heat and pressure along the non-bonding zone to the back panel and the first closure panel and the remainder of the multi-panel assembly, the first closure panel is bonded to the remainder of the multi-panel assembly such that a second mode opening to the containment region is able to be created between the closure element of the back panel and the closure element of the first closure panel, and the perimeter of the second mode opening is defined by the two closure elements, and wherein each panel comprises multiple plies, the multiple plies comprise at least a first ply and a second ply, wherein the second ply is less stretchable than the first ply, and the first ply is bondable to another panel of the multi-panel assembly under an application of heat and pressure. a front panel and back panel sealed at a base of the bag and two sides extending from the base to define a containment region, the bag being open or openable at an opening region opposite the base and where a multi-panel assembly is provided comprised of said front panel and back panel, at least one side being of a gusset formation, a first closure panel comprising a closure element for cooperating with a closure element associated with the back panel to provide an openable and re-closable closure of the opening region, and a non-bonding zone at which the back panel and the first closure panel are prevented from bonding to each other under an application of heat and pressure, the non-bonding zone being located along the length of the openable and re-closable closure, and more distal of the base of the bag than the openable and re-closable closure, wherein in a first mode the first closure panel is associated with the back panel, and the containment region is accessible through a first mode opening the perimeter of which is defined by the front panel and back panel and two sides, and wherein in a second mode, following an application of heat and pressure along the non-bonding zone to the back panel and the first closure panel and the remainder of the multi-panel assembly, the first closure panel is bonded to the remainder of the multi-panel assembly such that a second mode opening to the containment region is able to be created between the closure element of the back panel and the closure element of the first closure panel, and the perimeter of the second mode opening is defined by the two closure elements, and wherein each panel comprises multiple plies, the multiple plies comprise at least a first ply and a second ply, wherein the second ply is less stretchable than the first ply, and the first ply is bondable to another panel of the multi-panel assembly under an application of heat and pressure.