For example, the thin walls of standard moving boxes cannot withstand the multiple transfers, stacking and other rigors of the shipping / mailing process. Further, failing to pack the boxes fully may result in boxes that "cave in" when other boxes are stacked on them. Mail Storage companies often request customers to use thick walled or reinforced shipping boxes, to reinforce the seams with heavy duty packing tape, and to pack boxes to their fullest (while not over-stuffing them).