Most 3D printing filaments (ABS, PLA, PETG, PETT, PC and Nylon) are hygroscopic materials, which have a strong affinity for moisture. When being exposed, these filaments readily absorb moisture in the air. The migration of moisture into the filament occurs over time and will eventually slow and stop when the moisture content reaches a state of equilibrium with that of the surrounding air. At the equilibrium point, the moisture content in the filament will be evenly distributed throughout the entire filament’s interior. Actually the water molecules inside the filament are attached to the polymer molecule chains, forming a strong inter-molecular bond. This bond is what makes drying the filament difficult. If the moisture is not extracted from the filament, even a small amount of moisture in the filament can cause streaks, bubbles, burning, brittleness and even a chemical reaction (hydrolysis) when the filament melts, passing through the heated nozzle. When this happens, the filament will make a popping/cracking/hissing sound and the 3D prints will have rough/grainy surface finish with much reduced physical properties (less tensile and impact strength). In some cases, the printing just fails due to: (1) the print not sticking to the build plate; (2)severe warpage; (3)intermittent inter-layer bonding; (4)jammed nozzle. In addition, the moisture content in the filament will turn into steam and evaporate, releasing a lot of plastic pollutants into the air. Many of us have experienced that a new filament prints very good in the beginning, but regularly fails after few months in storage.