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 RSC boxes are the same depth, and the two outer flaps (normally the lengthwise flaps) are one-half the container’s width so that they meet at the center of the box when folded. The only overlaps in this design are the flap for a glued or stitched manufacturer’s joint, and the inner (or minor) flaps. A fill-in pad can be put between the two inner flaps to create a flat, even bottom surface.