Standard shipping boxes are made of corrugated cardboard for storing and shipping products. They come in a variety of different sizes and shapes to accommodate many kinds of products. Box strengths vary, but 200# and 32 ECT are common strength ratings. Boxes labeled 200# provide more protection against bursting and are stronger for stacking than boxes labeled 32 ECT. Shipping boxes have flaps or lids that close at the top or side, securing items inside.