What is Paper Curl?

Paper and cover curl can occur due to fluctuations in relative humidity (RH) within the environment where the books are situated. Ideally, paper remains flat at around 45%RH. Print shops regulate humidity levels by adjusting moisture levels in the air to maintain this target.

Paper and cover curling arises when RH shifts by 10% in either direction. Should RH drop by more than 15%, it may result in what's referred to as "ocean" curls, resembling waves on paper. This phenomenon can disrupt the print production process, necessitating precise humidity control in printing, binding, and paper storage areas. Paper and cover curling is independent of paper weight or quality; all paper and board stocks are susceptible to curling if RH deviates from the safe zone, even heavy board stocks.

RH fluctuates with outdoor temperature, air moisture content, and geographic location. Over time, books may acclimate to their environment, and covers may flatten again. To aid in this process, it's advisable to keep books in boxes or neatly arranged on bookshelves. However, extreme climates such as deserts or tropical regions may not be conducive to paper storage. If you have any inquiries, please don't hesitate to reach out to our OnPress support team.