U-Packs Triwall (7 Ply) boxes are strong enough to be a substitute for wood. These boxes are traditionally used for shipping heavy duty items such as metal parts, chemicals, export, etc. This type of corrugated design is commonly used for larger containers. At U-Pack, Triple Wall boxes are the strongest form of a corrugated case made from heavy duty board. The white colour of the top Kraft paper imparts the boxes a premium look and feel to these 7 Ply cartons.