What is Web Growth?

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Project Description

Have you seen a book with inside pages extending further than the cover?
Initially, you might assume that your printer trimmed the cover incorrectly or maybe there was an error during the binding process. However, what you are seeing was most likely not a mistake or intentional, but it was web growth.

Web growth is a common problem when text pages are run on a heatset web press. It refers to web paper changing sizes after the final trim in the bindery. As paper is hygroscopic, it is capable of absorbing or losing moisture depending on its environment. When paper fibers are exposed to moisture fluctuations, they contract and expand. This means that when paper loses moisture it will contract and decrease in size; when it absorbs moisture, it will expand and grow in size.

Web growth occurs when the signatures of the text pages are subjected to high temperatures in the heatset dryer unit which causes the paper to lose moisture and shrink. After the signatures have dried, the paper conditions to achieve relative humidity equilibrium which then absorbs moisture and expands the pages. The end result is a book with web growth. When the paper fibers contract and expand, it does so against the grain of the sheet which is why the book block appears to grow only on its face-edge and not the head and foot.

While its a very prevalent issue, there isn’t much that can be done to prevent it entirely. However, you can design around it and add a bleed-edge in a similar color to the cover so it’s not as noticeable.

For more information, please contact us.

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