Hygroscopicity in 3D printing: what it is and how to deal with it

Hygroscopicity is the invisible killer of 3D prints. Find out what it is, its effects on printing, and how you can avoid it!

Have you ever printed with old filament or material that has been exposed to moisture? If you have, you've probably encountered print quality issues. This is most likely due to hygroscopicity, which in terms of 3D printing is the appearance of a filament absorbing moisture.

Most threads are naturally hygroscopic - some more than others. This means that when there is moisture in the air (humidity), the thread naturally absorbs it. Although it is difficult to notice in advance, hygroscopicity is a factor that negatively affects the quality of 3D printing.

The moisture in the print material can't be seen, but when you heat it in the hot end of a 3D printer, you can. Essentially, the water boils as the filament melts, and this causes bubbling.

In this article, we'll take a closer look at how hygroscopicity affects print quality, which materials are hygroscopic, which are less so, and how you can prevent hygroscopic spoilage of your prints.

Effects on print quality

^{Can you guess which print was made with dry filament? (Photo: bobstro via Prusa Research)}

When the hygroscopic material absorbs moisture, printing with the "wet" filament can lead to an abundance of printing errors. Some of the most common signs of a wet floss include the following:

• Bubbles or spots in print layers;
• Stringing;
• Jamming in the extruder;
• Fragile filament, soft and fragile parts;
• Poor bed adhesion
• Extrusion problems

If you look at the picture above, you can see the difference between wet filament printing (bottom) and dry filament printing (top).

This does not mean that the wet thread can be  the only one cause of these problems, but it is among the most likely and should be one of the first aspects to check before looking at the machine itself.

Now that we know what can happen, let's take a closer look at which threads are more hygroscopic than others.

Most affected materials

^{Polyamide (PA/Nylon) is a very hygroscopic thread (Source: ontopathogenic_ via Reddit)}

As mentioned above, many of the materials used for 3D printing filament are somewhat hygroscopic. This shows how quickly different materials absorb moisture - it varies. The following materials are most likely to get wet quickly:

• Nylon and other polyamides (PA)
• PVA (often used as a support material)
• TPU
• PLA
• ABS
• Polycarbonate (PC)
• PETG
• Many flexibles

For anyone interested in diving deeper, BCN3D conducted research on the effects of humidity on 3D printing filaments and released a white paper detailing their findings. They mainly looked at the three most hygroscopic filaments in their portfolio, namely PA, PVA and TPU. Of the three, PVA absorbed the most moisture during their experiments, and TPU the least. That being said, TPU fares worst when it comes to its resistance to poor storage conditions.

Which are less hygroscopic?

Compared to the materials listed above, the following are less prone to hygroscopic problems:

• ASA
• Polypropylene (PP)
• HIPS (most commonly used for support material ABS)

That doesn't mean they won't absorb moisture – they will, but not as intensely or as quickly as the materials mentioned above.

Prevention is always warranted, no matter what filament you have. So let's look at what can be done to limit the exposure of your strands to moisture.

Filament storage

^{Using a dry box (or separate ones) can keep the threads… dry (Source: Austin via Printables )}

Knowing the common symptoms and the main culprits, let's talk about how to actually deal with hygroscopicity. Naturally, the first step is prevention, i.e. proper storage.

Generally speaking, the key is to store the thread in a dry, watertight container. You should do this as often as possible between prints.

A solid storage option is a dry box, which will physically separate your thread from the environment. This method works for both long-term and short-term storage as long as there is some kind of watertight seal on the opening. Note that there is a difference between dry box (which keeps the environment… dry) and drying box , which actively heats the thread to remove moisture.

If you want to store thread for up to a few days, a tightly sealed bag will do a good job. In this case, consider using desiccants to remove oxygen and moisture.

Depending on the storage option you choose, whether it can be purchased or DIY, you may want to consider a design that includes an opening (while still keeping the box airtight). This will allow you to use the thread while it is stored.

Thread drying

^{PVB is hygroscopic so dry it before printing (Source: random-builder via Thingiverse )}

Printing with filament that is stored in a dry box is a great idea to prevent problems related to hygroscopicity. But if you haven't been vigilant about storing the material properly, it's likely absorbed some moisture from the air, especially if you've had it for a long time.

The good news is that you don't need to buy another reel. Rather, you'll need to find out if your thread is wet and, if so, dry it.

Wet thread detection

To determine if your thread is "wet" you need to pay attention to how it prints. A wet filament often results in lower than expected print quality.

If a spool of thread has absorbed a decent amount of moisture, you can do a simple test. All you have to do is thread some thread through the nozzle and listen carefully. You'll know you have wet filament if you hear a crackling/popping noise as the filament is extruded. Another indication is if you see steam coming out of the print (hot meets cold) or any of the print issues mentioned above.

Thread drying

You've done the tests and your thread is wet. It's time to dry it.

Actually drying the thread is easy. Just put the spool in the oven and for PLA set the temperature to around 40-50 °C. Then leave it there for about 4-6 hours. Other materials, such as ABS and Nylon, will benefit from higher temperatures (~80 °C). You can check Bambu Lab's suggested temperatures for more materials, but it is always recommended to consult the manufacturer's advice.

Also, avoid over-drying your strand as this can lead to brittleness.

If the oven is not an option, you can choose a drying box. Creality's Dry Box 2.0 and Sunlu's FilaDryer S1 Plus are great options, but you can also take a DIY approach.

If you need further explanations, how to save yourself from moisture in your materials, which material to use for your projects or other case studies in additive technologies - do not hesitate to contact us:

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