3-ply corrugated stock has one sheet of flute glued in between two sheets of paperboard.  This type of corrugated stock is widely known as ‘single wall corrugated stock’ and is the most common choice for making cost-effective corrugated boxes and inserts.  On the other hand, 5-ply corrugated stock has two sheets of flute alternatively layered between three sheets of linerboard.  Also known as ‘double wall corrugated stock’, this version of corrugated stock is sturdier and is suitable for heavier products.