The sides of the can were marked with cross-like indentations that strengthened the can while allowing the contents to expand, as did an air pocket under the handles when the can was filled correctly. This air pocket allowed the container to float if dropped in water. Rather than a screw cap, the containers used a cam lever release mechanism with a short spout secured with a snap closure and an air-pipe to the air pocket which enabled smooth pouring (which was omitted in some copies). The interior was also lined with an impervious plastic, first developed for steel beer barrels, that would allow the can to be used for either water or petrol. The can was welded and had a gasket for a leak-proof mouth.