Complete Sizes of Vented Caps Closures. They are used in the 20-liter plastic jerry cans,55- gallon or 200-liter plastic drums, and IBC tote top lids. The advanced vented structure allows the passage of gas molecules but does not allow water molecules to pass through. In the transport process, the vented caps closure can release the pressure of the drums, at the same time vented caps closure also protects the contents of the drums not being polluted. Thus making transport safer and cleaner. The following just shows the popular type of hot sale. Please contact us for more styles and designs.