During the papermaking process, the materials used for printing are typically produced using either a long screen machine or a modified rotary screen machine. Both types of machines play a crucial role in shaping the paper sheet as it forms.
Regardless of whether it's a long screen or a round screen machine, the paper is always in contact with the screen on one side and a felt on the other. This interaction leads to two distinct surface characteristics on each side of the paper.
The side that comes into direct contact with the screen, which often retains visible mesh marks, is referred to as the "back" side. The opposite side, which appears smoother and more uniform, is known as the "front" side. These differences are not just cosmetic—they have a real impact on the paper’s performance.
The main cause of these differences lies in the uneven distribution of fillers and short fibers between the two sides. When pulp with about 1% consistency flows onto the wire section of the paper machine, a large amount of water is removed during this stage. As the water drains, many fillers and fine fibers are also lost. While they can be evenly distributed on the front side where there is a lot of water, the middle and tail sections of the wire, which contain less moisture, result in fewer fillers and fibers remaining on the back side—especially where the paper is in contact with the screen.
Another factor contributing to the distinction between the front and back sides is the contact with the screen during formation. Due to the high plasticity of the pulp, the texture of the screen can leave visible impressions on the paper. The pulp flowing onto the screen has around 1% consistency, and to enhance the water removal process, there are press rolls and suction boxes beneath the screen. This pressure forces some of the pulp into the screen’s mesh, creating a pattern that remains even after pressing and drying.
The presence of front and back sides affects more than just appearance. It influences the paper’s smoothness, gloss, absorbency, ink absorption, and even its tendency to curl. These factors are especially important in printing applications where consistent quality is essential.
In most cases, the front and back sides of uncoated paper can be identified visually. The side with visible mesh marks is considered the back, while the side with a clearer, more uniform texture is the front. However, in some cases, additional testing may be required to determine the correct side for specific uses.
Understanding the difference between the front and back of paper is essential for ensuring optimal print quality and performance. Whether you're working with standard printing paper or specialized stock, knowing which side to use can make a big difference in the final outcome.
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