If your prints have started stringing, popping, or snapping for no obvious reason, the filament itself is probably the problem. Most FDM materials are hygroscopic, pulling moisture out of the air and into the polymer, while ambient temperature swings compound the damage in storage and in the print chamber. Here's what's actually happening at the material level, and where to draw the line before a spool becomes scrap.
Moisture: The Bigger Threat
Nylon, PVA, TPU, and PETG absorb ambient water vapor aggressively. PLA and ABS are more forgiving but still degrade with prolonged exposure. Once water is trapped inside the filament, it doesn't just sit there — at typical nozzle temperatures (190–260°C), that water flashes to steam and expands roughly 1,600x in volume.
That steam has to go somewhere, and it goes through your nozzle mid-extrusion. The result:
- Audible popping or crackling as the filament extrudes
- Visible steam or wisps at the nozzle tip
- Stringing, surface bubbles, and a rough or brittle-looking finish
- Reduced layer adhesion and lower tensile strength — the steam leaves voids inside the print
- Nozzle clogs in severe cases
Hydrolysis: The Damage You Can't Dry Out
This is the part that trips people up. Drying a wet spool restores printability, but it doesn't undo everything. At high temperature, water chemically attacks the polymer chains in PETG, nylon, and TPU through hydrolysis — the chains break, and tensile strength drops permanently, even after the filament tests "dry" again. PLA is comparatively resistant to hydrolysis. PETG and nylon are not, which is why a nylon spool left out overnight in humid air can turn brittle in ways a dryer cycle won't fix.
Safe Storage Humidity by Material
| Material | Safe storage RH | Issues appear after | Recommended drying |
|---|---|---|---|
| PLA | 30–40% | ~1 week above 40% RH | 45–50°C for 4–6 hrs |
| ABS | 30–40% | Similar to PLA | 60–70°C for 2–4 hrs |
| PETG | 20–30% | ~3–4 days above 30% RH | 65°C for 4–6 hrs |
| TPU | 15–30% | ~2 days above 25% RH | 60–70°C for 4–6 hrs |
| Nylon | 10–20% | 12–24 hrs above 15% RH | 80–90°C for 8–12 hrs |
As a general rule, all common filaments stay print-ready for months when kept below 20% RH. Nylon is the outlier — a few hours of exposure in a humid shop or garage is enough to compromise a spool.
Temperature: Two Separate Problems
Temperature affects filament in storage and during the print itself, and the mechanisms are different.
In storage, heat accelerates polymer degradation independent of humidity, and can soften or deform spools left somewhere like a hot garage, a car, or next to a heated bed enclosure. Warm air also holds more water vapor, so a hot, humid storage spot compounds moisture uptake faster than either factor alone.
During printing, ambient chamber temperature matters most for warping-prone materials — ABS, ASA, nylon, and polycarbonate. Insufficient or uneven heat in the build chamber causes layer separation, cracking, and warping as outer layers cool and shrink faster than the core. That's the entire reason enclosed, heated-chamber printers exist. PLA is far less sensitive to this and prints fine in an open frame at room temperature.
Practical Mitigation
- Store filament in sealed containers or vacuum bags with desiccant, not the cardboard box it shipped in.
- Run hygroscopic materials (nylon, TPU, PETG) through a dry box or filament dryer before — and ideally during — printing, feeding through a PTFE tube to prevent reabsorption mid-print.
- Keep enclosure ambient temperature stable and matched to the material: roughly 40–60°C for ABS/ASA, higher tolerances for nylon and PC.
- Don't rely on a single spot-check with a cheap hygrometer. Drift happens between checks, and by the time you notice a problem in the print, the spool may already have crossed the hydrolysis threshold.
Monitor Your Environment with Atykai
Spot-checking a dry box with a $10 hygrometer tells you the humidity right now — it says nothing about the three hours it spent creeping past 30% RH while you were at work. A continuous temperature and humidity sensor placed inside your filament dry box or printer enclosure logs conditions minute-by-minute and alerts you the moment RH drifts out of range, before it shows up as a failed print or a brittle nylon part. Browse the SensorPush HT1 or, for water-resistant enclosures, the HT.w to find a sensor that fits your dry box, enclosure, or print farm setup.
What's your current dry box setup — desiccant and a hygrometer, or a dedicated dryer? Let us know what's been failing on you.