It’s important to keep your ABS resin pellets as dry as possible to prevent defects within the filament when extruding. Moisture related issues can be overcome by keeping the resin dry which will result in structurally stronger and fewer rejected prints.
ABS is slightly hygroscopic, which means that it absorbs moisture on the pellet surface. If a dry ABS pellet is exposed to humid air, moisture migrates into the pellet unit the moisture content is in equilibrium with the water content in the air.
Packaging can vary in its ability to keep moisture out, boxes and drums with polyliners tend to offer the best protection. Moisture absorption is reversible, if you leave your pellets in a low humidity environment, the pellets will loose water into the atmosphere.
The optimal target dryness for ABS resin pellets is 0.02.