What is Fluting in Web Printing?

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Fluting is the effect that happens to a web of paper when it passes through a dryer and a wavy look occurs.  This ripple effect tends to make the paper as if it it has parallel ripples.  The web offset heatset drier is the point that it happens.  

Fluting is a parallel ripple effect that occurs
on a web printing press.


Factors that contribute to fluting.

There are three main factors that are factors in the degree of fluting:
  1. Paper weight.  Much lighter uncoated stocks tend to have more fluting.  This is exacerbated when there is a lot of coverage. Additionally, the moisture content of the paper when it is produced at the mill is a factor.
  2. Ink coverage. Since paper shrinks in the web press oven, the heavier coverage areas will react differently than the areas with no coverage. The heavier coverage areas will dissipate the moisture and shrink like all other areas, but the ink will prevent it from doing so uniformly.
  3. Paper type. Uncoated lightweight stocks tend to show more fluting.  However even thicker products, such as 12pt will exhibit fluting under the right conditions.

How fluting happens.
It is a combination of the paper type, water, and ink.  But the biggest factor is the paper.  There is really no way to know how the paper will react until it has been run through the press. Even then, roll can differ from roll depending on moisture content and production run from the paper mill. 

How can fluting be eliminated?
Generally it cannot. But some web printing presses have had success by the following:
1. Switch paper rolls to a different production day from the mill. 
2. Adjust dryer temperature. Sometimes this can minimize fluting.
3. If it is occuring in a high coverage area, run the ink density in the lower end of the acceptable range.

Besides this, the only measures that can be taken are preventative. This might include not having high solid ink coverage on a cover and its backside to avoid the risk. For instance, a magazine designer may choose to not have a high coverage ad on the backside of the front cover. 

Designers might also consider having their heavier coverage pictures line up with one another. This is from the perspective of being all in line as it is running through the web press. 

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