A machine for forming bags of gussetted flat heat sealable web stock, opening the formed bags and drawing them down over palletized loads preparatory to conveying the same into an oven where the bags shrink into intimate contact with the load. The bags are opened by suction cup and claw assemblies mounted on the ends of arms that project from hinged carrier frames between which the palletized load is placed to be enwrapped. The frames swing towards and from one another, and in their innermost positions bring the suction cups into contact with the side panels of the pendently hanging web. This causes the suction cups to attach themselves to the side panels, and that attachment brings about initial retraction of the suction cups. With the side panels held by the suction cups, the claws are actuated to cause them to penetrate and grab the side panels. Outward swinging motion of the carrier frames and downward travel of the arms that carry the suction cup and claw assemblies opens the bag and draws it down over the load.