Introducing moisture into the sublimation process can cause unwanted results. Under normal circumstances, the small amount of moisture that can accumulate in the paper is absorbed directly into the transfer substrate. However, hard substrates such as metal and ceramic are unable to absorb excess moisture.
During production with a heat press operating at 400 degrees, that moisture can flash to steam and literally blow away the dye. Some of the problems that are attributed to moisture include: color shifting (colors lose accuracy), image bleeding, and uneven transfer of solid filled areas.
To minimize moisture issues, protect the paper from moisture absorption. Store paper in a dry place and consider using a sealed container or a Ziploc bag.
If you suspect moisture, set the paper on your press for a few seconds. Do not press it, just expose it to the warmth. The heat that radiates from the press should help evaporate most of the moisture.
—Jimmy Lamb, Sawgrass Ink