Our Extra Heavy-Duty Shipping Boxes (Double Wall, .5” thick) with two layers of corrugated provide unmatched strength and protection. If our standard corrugated or heavy-duty corrugated shipping boxes aren’t strong enough, or you need to provide extra protection to your product, choose one of these extra heavy-duty double wall shipping boxes. Box contents should not exceed 150 lbs. Boxes meet ASTM-D5118. Manufactured from Heavy-Duty 275#/ECT-48 kraft corrugated.