Our 20" x 20" x 20" Heavy Duty Multi-Depth Corrugated Boxes are super strong and heavy duty 275# Single Wall/ECT-48 kraft corrugated carton with twice the protection of a standard carton. ECT stands for "edge crush test". These Multi-Depth Heavy Duty Cartons are sold in bundle quantities and ship flat to save on storage space and shipping. 20 x 20 boxes with heavy-duty construction provide greater protection and is perfect to use when extra stacking strength is required. Variable depths at 20'', 18'', 16'' and 14''.