The Optimist buoyancy bags from Optiparts are made of polyurethane-coated nylon and are about half the weight and significantly stronger than buoyancy bags made of PVC or PVC-coated nylon. Some bags are available with a twist-lock tube valve. This valve is attached to a piece of tubing. With this valve, the bag can easily and quickly be inflated and deflated.SpecificationsMaterial: Polyurethane-coated nylon – lighter and harder PVC-coated nylonColour: GreySize inflated: 27 cm x 88 cmSize deflated: 41 cm x 100 cmRadius: 24 cmCapacity: 43 LPlease NoteNot to overinflate the Optimist buoyancy bags. When bags are properly filled, they will be soft to the touch. Over-inflated bags may burst when heated up by the sun or rising temperatures. Make sure there are no sharp points in your boat that would snag or puncture the buoyancy bags.