Optiparts air bags are made of heavy duty Polyurethane coated nylon. About half the weight and significantly stronger than bags made of PVC or PVC coated Nylon, they are compliant with IOD'95 rules. Available in normal valve or twist lock tube valve. 48 Liter bags are slightly heavier than 43 Liter bags, but after a capsize there is a lot less water in the boat. Easy to inflate and deflate, don't get caught on the water without them.