Heavy duty construction provides greater protection and stacking strength. Cartons are sold in bundle quantities and ship flat to save on storage space and shipping. Heavy-Duty boxes provide added protection to ensure that your shipments arrive safe. Weight: 1. 63. Corrugated cartons are all 100% recyclable. Double-wall boxes provide maximum stacking strength. 275# Double-wall/ECT-48 (Edge Crush Test) - holds up to 100 lbs. Industry Standard Double Wall Corrugated. Manufactured from 275# DW/ECT-48 kraft corrugated. Twice the protection of a standard carton. Our double wall corrugated boxes are created with two layers of fluting along with the 5-ply construction for providing extra strength. This helps you store heavy items easily as they have a high level of rigidity.