Pillow Bags are totally enclosed, with over-pressure valves to vent expanding air as they ascend. The advantage of Pillow Bags over the Open Bottom Bags is that they are excellent for raising sunken boats, and for towing jobs. Like the Boulder Bags and the Ocean Salvage Tubes, all Pillow Bags come with brass quick-disconnect fillings attached to a short filler hose (connects to 1/4" pipe thread)