Packaging Corp. of America is one of the largest producers of containerboard in the United States and also one of the largest manufacturers of corrugated packaging products. The company produces corrugated containers as well as the containerboard used to manufacture corrugated containers. Corrugated containers are the most commonly used type of paper packaging. Corrugated containers, referred to as cardboard boxes, are made by combining multiple layers of heavyweight paper known as containerboard and fabricating them into finished boxes.