Containerboard is the material used to make corrugated boxes – commonly known as cardboard. It is the most frequently used packaging material because it is versatile, lightweight, strong and made from a renewable resource. It is also the single most-recycled packaging material: in 2020, 88.8 percent of cardboard was recycled. More than half of recovered fiber used in manufacturing paper and paperboard in the U.S. goes into making containerboard.1
What is Containerboard?
Walls of corrugated boxes made with containerboard consist of two main parts: linerboard (or facing) and corrugated medium (fluted paper). The flutes in the corrugated medium form a series of connecting arches. An arch with a certain curve can support many times its own weight, especially when the ends of the arch are anchored. In corrugated containers, they are anchored to a facing. A vertical sheet of linerboard, used as the skin or facing, can support a weight greater than itself if it is held in place. Most linerboard is produced using softwoods, which have the longest fibers, and produce the strongest paperboard. The fluted corrugating material helps it stay in place, while the facing, in turn, protects the flutes from damage.
What Kinds of Products Are Made from Containerboard?
Containerboard is primarily used to make packaging. Boxes made from containerboard range in strength based on the combination of linerboard and medium. For example:
- Single wall: two sheets of linerboard with corrugated medium in the middle
- Double wall: three sheets of linerboard with two corrugated mediums in between them
- Triple wall: four sheets of linerboard with three corrugated mediums in between them
Boxes are used to protect, store and transport a variety of goods – from the items you buy online that arrive on your doorstep to bulk produce delivered to your local grocery to large and fragile items such as televisions and appliances.
The first use of corrugated paper for packaging came in 1871, when an American, Albert Jones, introduced an idea of wrapping bottles and glass chimneys in it. It was the addition of a liner to one and then to the other side of corrugated paper that signaled the birth of corrugated boxes.
Why Use Containerboard?
Containerboard is Strong
Corrugated is designed to be stacked, to withstand top and side pressure and is crush resistant. It is impact-, drop- and vibration damage-resistant, and can be customized for added protection. It is lightweight while having a high strength-to-weight ratio. Packaging can be designed to move bulk products, ship individually packaged liquids or even transport hazardous materials.
Containerboard is Convenient
Corrugated containers are relatively lightweight and they can be broken down for easy transport. Moreover, containerboard can be cut and folded into an infinite variety of shapes to ensure a product is uniquely presented but also protected. Branding can be directly applied to the surface of containerboard. It is also cost-effective as the overall cost of using corrugated for shipping is a small portion of the value of the goods being shipped.
Containerboard is Sustainable
Corrugated containers are made from a renewable resource – recovered paper and trees that are replanted to ensure a sustainable supply. The U.S. grows more wood than it harvests. There are 20 percent more tress in the U.S. now than there were in 1970. According to the U.S. Environmental Protection Agency (EPA), paper and paperboard packaging, which includes containerboard, accounts for nearly three-quarters of packaging materials recovered for recycling in the U.S. That is more than any other packaging material.
How is Containerboard Made?
The first step in the process is to make pulp. Pulp can be made from either virgin fiber, which are wood chips, or from recycled paper products.
Wood chips (virgin fiber) are cooked using a chemical process in essentially a pressure cooker known as a digester. The wood fiber is separated into cellulose fibers, lignin (the wood glue that holds the tree together) and other substances such as sugars. Cellulose is an essential building block in the cell walls of trees and plants, helping to make them strong. The pulp is then washed to clean it and separate it further from the other tree components. After the pulp is washed, it is screened for further cleaning.
For mills using recycled materials, pulp is made by mixing the recovered fiber with water in what resembles a large blender called a repulper. In the repulper, the pulp is separated to create individual fibers in a slurry. From there, the pulp is washed and screened to further separate the fiber from other debris like dirt.
The pulp, which maintains its natural brown color, then needs to be formed into a sheet by the paper machine. At the wet end of the paper machine, the pulp flows onto a moving endless belt with a screen to filter out water and form a web. Further down the line, in the press section, the pulp, which looks like a brown sheet, goes through several presses to further remove excess water. At this point the web of material still must shed water, so it passes into a dryer. The dryer is a large cylinder and uses steam to dry the pulp. The wet web of pulp is pressed against the cylinder tightly to dry it through evaporation, providing a consistent thickness prior to the paper being processed into a giant roll. Paper formed in this process can now be used as the inner and outer liners on a corrugated box.
Next, the rolls of paperboard are shipped to a converting facility, so they can be made into boxes. The flutes are manufactured in a corrugator machine and glues the tips of the flutes to the linerboard. Corrugated medium is fed into the corrugator and the rollers heat the paper to a specific temperature. Then the medium is fed into the single facer, which creates the arches of the flute and adds a starch-based glue on one side of the tips of the flute. The flute is glued onto the inner liner. Next, the outer liner is glued, and the paper is heated so the glue bonds securely. This process is altered based on the wall size of the corrugated container, meaning if it is single, double or triple walled in addition to the size of the flute. After the inner and outer liners are glued to the flute, the product is cut to specification based on the order.
1 AF&PA Statistics