We’ve all had to deal with irate editors complaining about the cover being narrower than the book block, and we all know the answer is always “moisture”.

Here’s a neat little video from Edwards Brothers Malloy which explains the phenomenon. Unfortunately while we know why it happens it seems we are still trying to figure out how to prevent it.

In the olden days, when heat-set wasn’t a factor, and everything took longer, printed sheets got to lie around for a while, waiting to get onto the folding machine, and then into the gathering line. As a result this problem was rare.