Most filament spools come in airtight bags to protect them from moisture. When you open such packaging—or if the filament wasn’t delivered in a sealed, airtight bag in the first place—follow these simple guidelines to prevent your filament from degrading.
Overview
Most filament materials are, to some degree, hygroscopic—they absorb moisture from the surrounding air over time. Wet filament can lead to degraded print quality, including stringing, bubbling, or weak layers which is why you should make sure your filament is kept in low humidity.
There are varying approaches to managing filament storage:
- Filament Dryers: Actively remove moisture from filament.
- Airtight Containers: Store filament with silica gel for passive drying.
- Unprotected Storage: Leaving filament exposed to room air—often leading to issues.
The impact of moisture depends on:
- Relative Humidity (RH) in the environment.
- Filament Material and its susceptibility to moisture.
Highly hygroscopic materials (e.g., PVA, Nylon) require strict moisture control, whereas others (e.g., PLA) are more forgiving but still benefit from proper storage.
Material Comparison Table
| Filament | Hygroscopy | Speed of Absorption | Effects of Moisture During Print | Resilience to Storage in High Humidity |
|---|---|---|---|---|
| PVA (Water-Soluble) | Very High | Very Fast | Severe bubbling, poor adhesion, unusable | Very Low |
| Nylon | Very High | Fast | Stringing, bubbles, weak layers | Low |
| PVB | Very High | Fast | Surface imperfections, weak adhesion | Low |
| PC (Polycarbonate) | High | Fast | Bubbles, cracks, weak layers | Low |
| PETG | Moderate to High | Moderate | Stringing, bubbles, reduced clarity | Moderate |
| TPU | Moderate to High | Moderate | Stringing, inconsistent extrusion | Moderate |
| Wood-Filled | Moderate to High | Moderate | Swelling, inconsistent extrusion | Low |
| PLA | Moderate | Slow | Brittle filament, minor surface issues | Moderate |
| PLA+ | Moderate | Slow | Brittle filament, minor surface issues | Moderate |
| ABS | Low | Slow | Minimal (only under very high humidity) | High |
| ASA | Low | Slow | Minimal | High |
| HIPS | Very Low | Very Slow | Negligible | High |
| PP (Polypropylene) | Very Low | Very Slow | Negligible | High |
| PEI/ULTEM | Very Low | Very Slow | Negligible | High |
| Carbon Fiber Composites | Low to Moderate | Varies | Minimal (depends on base material) | Varies |
Hygroscopy refers to a material’s affinity to water. The Speed of Absorption indicates how quickly a material absorbs moisture—Very Fast means significant absorption occurs within hours.
Storage Recommendations
General Guidelines
- Use Airtight Containers: Store spools in plastic containers with airtight seals.
- Include Desiccants: Add silica gel packs to absorb residual moisture.
- Monitor Humidity: Use a small digital hygrometer to ensure RH stays below 30%.
- Avoid Problem Areas: Don’t store filament near windows, heaters, or damp areas (e.g., basements).
Passive Drying
Passive drying prevents moisture absorption using desiccants, like silica gel, without applying heat.
- Use Color-Changing Silica Gel: Monitors saturation levels (e.g., orange → green or blue → pink).
- Silica Gel Requirements: 20–30g per spool for optimal effectiveness.
- Regeneration: Heat silica gel in an oven at 100–120°C for 2–3 hours.
Ideal Conditions: Maintain relative humidity (RH) below 30% and temperature between 15–25°C.
Quality sellers ship their spools in airtight plastic bags and include small silica gel packs. Do not throw these away. They are designed to attach to your print spools and help keep humidity levels low, particularly when you store the spools in an enclosed container:
Bulk Silica Gel
You can also purchase silica gel in bulk for larger-scale humidity control:
Silica gel is often color-coded to indicate its moisture level. It starts orange when dry and turns blueish once saturated. To regenerate it, heat the silica gel to 100-120°C in an oven until it dries out.
DIY Silica Containers
Many electronic components, such as displays and boards, come in small plastic containers that can be repurposed as silica gel holders. To make one:
- Ensure the container is large enough to hold 20g to 50g of silica gel.
- Drill a large number of ventilation holes into the container. The holes should be smaller than the silica gel pieces to prevent spillage.
If you decide to place silica gel in an extra container, it is crucial to drill enough holes so that there is sufficient ventilation. The container in the picture managed to drop humidity in a plastic container at a rate of 5%/day, and even after 3 days, humidity in the container was still above 30% (so more holes are required). Pouring silica gel directly into the plastic container dropped humidity to around 10% in hours.
These DIY containers can be placed into the AMS (Automatic Material System) of your printer or any storage solution you use.
Plastic Boxes
Alternatively, consider plastic filament storage boxes. Generic plastic cereal boxes work well too:
With plastic boxes, you may want to fill silica gel right into it so it covers the ground, without bothering to place it into separate boxes. This works excellently, and due to the large surface area, humidity quickly drops to around 10%. Once the gel is eventually saturated (which is when it changes color and turns blueish), you can easily pour the silica into a container to regenerate it in an oven.
Monitoring Storage Conditions
To monitor humidity effectively, add a cheap electronic hygrometer to your storage box. This allows you to keep an eye on the humidity level and ensure optimal conditions for your filament.
Most cheap electronic humidity meters require one or two LR44 button cells. They are not always included.
For added convenience, you can install a ball-bearing filament support and create a small hole with a tube in the box’s cover. This setup allows you to feed filament directly to the printer while keeping the spools in low-humidity storage conditions:
Active Drying
If filament has absorbed moisture, active drying uses heat to remove it.
Once filament has absorbed significant moisture, you can no longer rely on passive drying with silica gel. At normal room temperatures, the diffusion process is not strong enough to effectively remove the moisture trapped in the filament. You now need to add heat to remove the moisture.
You can dry filament in any controlled hot environment as long as the air temperature stays below the filament’s glass transition temperature (Tg) to prevent softening or deformation which would permanently damage your filament and render it unusable.
Common methods include:
- Ovens
- Food dehydrators
- even Saunas are sometimes used
However, these methods often have limitations. Most ovens and food dehydrators lack precise temperature control, which can lead to uneven or ineffective drying. Additionally, such setups can be inconvenient for regular use and often are highly energy inefficient.
Dedicated Filament Dryers
To address these challenges, dedicated filament dryers are available. These devices come in various shapes and sizes and heat just as much room as is required to store the filament spool(s) you want to dry: some models can dry just one spool at a time, while others can handle two or even four spools simultaneously:
Advantages of Filament Dryers
- Precision: Filament dryers often include pre-programmed temperature settings for different filament types, eliminating the need to remember drying temperatures, and can maintain this temperature very precisely.
- Convenience: Many models come with a built-in timer, allowing for automated drying cycles.
- Continuous Protection: Most filament dryers allow you to feed filament directly from the dryer to the printer. This ensures the filament remains dry throughout the printing process.
- Improved Print Quality: Printing with pre-heated filament can enhance print quality, particularly at faster print speeds: pre-heated filament reduces the print head’s workload, minimizes friction in the tubes, and ensures smoother extrusion.
By combining proper storage, monitoring, and drying techniques, you can significantly extend the life of your filament and improve the quality of your 3D prints.
Drying Temperature Recommendations
| Filament | Drying Temp | Duration | Softening Point (Tg) |
|---|---|---|---|
| PLA | 40–45°C | 4–6 hours | ~60°C |
| PETG | 60–65°C | 4–6 hours | ~80°C |
| Nylon | 70–80°C | 8–12 hours | ~90–100°C |
| PVA | 55–60°C | 6–8 hours | ~60°C |
| PVB | 60–70°C | 6–8 hours | ~70°C |
| ABS/ASA | 70–80°C | 4–6 hours | ~90°C |
Lower temperatures work but take longer. For example, drying PLA at 30°C instead of 45°C will reduce moisture but take twice as long.
Environmental Humidity Thresholds
If airtight containers are unavailable, keep filament in low-humidity environments. Below is a summary of RH limits for safe open storage:
| Filament | Max Safe RH (%) | Notes |
|---|---|---|
| PLA | 30–40 | Absorbs slowly; safe for months at low RH. |
| PETG | 30–40 | Moisture causes stringing and reduced print quality. |
| TPU | 20–30 | Very sensitive; poor adhesion when exposed to moisture. |
| Nylon | 10–20 | Extremely hygroscopic; airtight storage is mandatory. |
| PVA | 10–20 | Requires sealed storage to avoid rapid degradation. |
| ABS/ASA | 30–40 | Resistant but benefits from dry environments. |
| PC | 20–30 | Moisture causes bubbles and weak layers. |
Summary
For best print quality:
- Store Filament Airtight: Use containers with silica gel to maintain RH below 30%.
- Dry Filament Actively: If moisture absorption occurs, use a filament dryer at safe temperatures.
- Monitor Your Environment: Avoid high humidity or temperature fluctuations.
Vacuum-sealing and using hygrometers further ensure your filament stays moisture-free.
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(content created Dec 13, 2024)