Use our Heavy Duty Corrugated Boxes to ensure your shipments arrive safe. You may choose between singlewall or doublewall corrugated. Our singlewall cardboard boxes are made from strong 275# or 44 ECT corrugated, and are approximately 35% stronger than standard boxes. Doublewall cardboard cartons are made from 275# or 48 ECT double wall corrugated, and are twice as strong as standard boxes. The sizes listed are all inside dimensions. Sold in bundle quantities.