Paper is very sensitive to changes in temperature and humidity. Excessive moisture will cause flat sheet paper to curl. The edges of roll paper for web presses will become slack if excess moisture is present. Many printing companies have temperature and humidity controlled environments to lessen the effects of changing weather conditions. It is almost impossible to print with paper that has curled or stretched because of poor conditions in the printing facility. Paper should always be ordered with enough lead time so that the paper has a chance to become acclimated to the temperature and humidity conditions of the printing facility. If you unload paper from a truck that has been in freezing temperatures and then bring it directly to a press to be printed upon, you could have problems. Once the paper is unwrapped in the warmer environment, it will immediately begin to pick up moisture if it has not been allowed to become conditioned to the humidity and temperature of the building. Some of this moisture will disappear as the paper becomes warmer, but the edges of the paper will still be damaged. It is necessary to leave the paper in its original wrapping and let it remain unopened until it becomes conditioned to the humidity and temperature of the pressroom and is ready to be used. The amount of time necessary for the paper to be conditioned properly can range from a few hours up to several days depending on the amount of paper and the difference in the temperature and humidity levels between the pressroom and the environment where the paper had been sorted previously. The chart below shows the number of hours necessary for this conditioning.

Number of Hours Necessary for Proper Conditioning