Heavy duty Optimist buoyancy bags. According to IOD'95 rules. Optiparts buoyancy bags are made of heavy duty polyurethane coated nylon. Special treatment for color fading and hydrolysis have been applied to guarantee long life. The Optiparts buoyancy bags for Optimist sailing are about half the weight and significantly stronger than bags made of PVC and PVC coated nylon. Some bags are available with a twist lock tube valve.