Most FDM/FFF filaments are hygroscopic – they absorb moisture from the surrounding air. When these water molecules are heated during extrusion they turn into steam, creating bubbles and voids inside the melted polymer. This foaming causes poor surface quality, inconsistent extrusion, weak layer bonding and ultimately weaker parts. Moisture can also catalyse hydrolysis, a chemical reaction that breaks polymer chains, further degrading mechanical properties. Even newly opened spools can contain significant moisture (e.g. > 0.75 % for many neat nylons), and hygroscopic materials like nylon can absorb up to 7 % of their weight in water.
Drying your filament before printing is one of the simplest ways to improve print quality and ensure parts meet their design strength. This guide gathers the latest research and manufacturer recommendations to explain why drying matters, which materials are most sensitive, how to dry filament correctly and how to store it to keep it dry.
When filament absorbs moisture the trapped water changes the way the polymer melts and flows. Common problems include:
Moisture also reduces the mechanical performance of printed parts. For example, drying continuous carbon‑fibre‑reinforced PA for two hours at 70 °C before printing increased tensile strength by about 15 % and flexural strength by 11.5 %.
Different filaments absorb moisture at different rates. Materials that are very hygroscopic require careful storage and drying; others are less sensitive but still benefit from drying before printing.
| Category | Materials | Notes |
|---|---|---|
| Highly sensitive | Nylon/PA, PVA/BVOH support filaments, TPU/TPE | Absorb large amounts of water quickly and need drying before each print. |
| Moderately sensitive | PETG, ABS/ASA, Polycarbonate | Absorb some moisture; drying improves surface finish and reduces stringing. |
| Less sensitive | PLA | Absorbs less moisture but can still become brittle or stringy over time. |
Use a dedicated filament dryer, food dehydrator or convection oven set to a controlled temperature. Avoid microwave ovens. Always cool spools in a sealed container after drying to prevent reabsorption.
| Material | Temperature (°C) | Time | Notes |
|---|---|---|---|
| PLA | 45–55 | 4–6 h | Improves brittleness and surface finish. |
| PETG | 55–65 | 4–6 h | Reduces stringing and bubbles. |
| ABS/ASA/PC | 70–80 | 4–6 h | Higher temperatures improve layer adhesion. |
| TPU/TPE | 40–55 | 5–12 h | Low temperature for a longer time. |
| PVA/BVOH | 50–60 | 6–12 h | Very hygroscopic; dry before every print. |
| Nylon (PA) | 70–90 | 8–12 h (longer for PA6) | Extremely hygroscopic. |
| Ultem/PEEK/PEKK | 120‑150 | 3–6 h | High‑temperature thermoplastics. |
Peer‑reviewed studies consistently show that moisture reduces mechanical properties. PLA blends conditioned at room humidity for several months lost 24–36 % of their tensile strength compared with dried samples. ABS composites stored at high humidity exhibited significant void formation and a drop in tensile strength. In contrast, drying continuous fibre‑reinforced PA composites before printing increased tensile strength by 15 % and flexural strength by 11.5 %.
Drying filament is a simple but critical step in achieving strong, accurate, professional‑quality 3D prints. By understanding how moisture affects different materials and following the best practice guidelines above, you can minimize defects like stringing and warping, maximize strength and dimensional accuracy, and protect your investment in expensive engineering filaments.
This guide synthesises information from manufacturer technical notes, 3D printing industry articles and academic research papers on the effects of moisture on thermoplastics. Key sources include: