Our 48" x 40" x 36" Heavy Duty Corrugated Boxes are super strong and heavy duty 275# Double Wall/ECT-48 kraft corrugated carton with twice the protection of a standard carton. ECT stands for "edge crush test".The Heavy Duty Double Wall 275#/ECT-48 Cartons are sold in bundle quantities and ship flat to save on storage space and shipping. 48 x 40 x 36 Heavy Duty Double Wall boxes with heavy-duty construction provides greater protection and is perfect to use when extra stacking strength is required. Designed to protect your large-size valuable items, fragile, or heaviest items.