Containers may be constructed of either single, double, or triple wall corrugated as required for strength. For double and triple wall, the flute sizes for each sheet of corrugated material are usually different. The strength of the box is increased when flutes are not perfectly aligned. Water resistance may also be specified. All flaps in OSC boxes are the same depth, and the two outer flaps (normally the lengthwise flaps) overlap by 1″ or more. The box is easily closed, with glue or tape over the overlap area. The style is used when the length of the box is considerably greater than the width, resulting in a gap between the inner flaps. The sealed overlap helps to keep the outer flaps from pulling apart.