While most plastics used in 3D printing are hygroscopic, including the very popular PLA, meaning that they can and will absorb moisture from their surroundings over time, PETG is especially notorious for absorbing moisture very quickly (unless it’s properly stored), making it critical to ensure that your spool is completely dry before printing with it to avoid problems.
In this guide, we will take you through various methods of drying PETG to make it moisture-free and ready to print, discuss how to correctly store PETG to ensure that it always stays moisture-free, even when you need to store it for prolonged amounts of time and explain how you can identify a spool of PETG filament that has absorbed moisture.
Drying PETG Filament & Getting Rid of the Moisture
While drying your PETG filament can seem challenging at first glance, especially if you didn’t have to dry any spools of filament until now, it’s actually a pretty standard procedure that won’t cause you or your spool of PETG any trouble as long as you’re careful.
Below, you can find four different methods you can use to dry PETG filament in a convenient manner, and pick out the one that you think will be most suitable for you based on the tools you currently have access to.
Drying PETG with a Convection Oven
Using a convection oven is perhaps the most common way of drying a spool of PETG, as it is an appliance you can find in practically every household, and it gets the job done in a straightforward and effortless way.
For this method, start by pre-heating your oven to 55 degrees Celsius / 131 degrees Fahrenheit, and wait until the pre-heating process is complete, as ovens can overshoot the temperature during pre-heating to reach the target temperature faster.
While using a temperature value slightly below the glass transition temperature (softening point) of the PETG you’re using will produce the best results, we believe that going above the 55 degrees Celsius / 131 degrees Fahrenheit limit introduces unnecessary risk due to most manufacturers not accurately specifying the glass transition temperature for the filament they’ve produced.
Once the oven is fully heated, verify the temperature, either with an infrared thermometer or a classic oven thermometer, and ensure that the oven temperature is stable at 55 degrees Celsius / 131 degrees Fahrenheit, as it’s possible for the temperature indicator on the oven to not be too reliable in some cases.
Finally, pop the PETG spool in the oven and let it dry for 6 hours, which should get rid of the moisture in most cases and make your PETG ready to print once again.
On the other hand, if the moisture is still there after drying, we recommend giving it a few more hours in the oven, followed by slightly increasing the oven temperature (no more than 5 degrees Celsius at a time, max 65 degrees Celsius) if that doesn’t help, and trying again.
Please note that the chance of the filament softening and practically becoming unusable will become higher as you increase the temperature – and while it’s unlikely that you’ll hit the glass transition temperature of your PETG at the 55-65 degrees Celsius range, it’s still a risk to be aware of.
Drying PETG with a Food Dehydrator
A food dehydrator is another kitchen appliance you can use to dry your PETG, and even though it’s not a device that you’ll come across as commonly as an oven, it’s slightly more user-friendly when it comes to the filament drying process due to there being less risk of softening the filament.
Similar to the oven method, start by setting the temperature of your food dehydrator to 55 degrees Celsius, and once it has fully warmed up, confirm the temperature with an infrared thermometer to ensure that it’s not overshooting, which is crucial to avoid a scenario where the filament ends up softening.
Once the food dehydrator is ready to go, pop your spool of PETG inside let it dry for 6 hours at a time; repeat this process until all the moisture is gone, and if moisture is still present, increase the temperature by 5 degrees Celsius at a time, up to a maximum of 65 degrees Celsius.
Bonus Tip: if DIY is your thing, you can convert your food dehydrator to a full-time filament dryer with some modifications, where the filament spool stays inside at all times to prevent moisture from affecting it in the time that it’s attached to your 3D printer (especially useful in humid areas), eliminating the need to buy a separate filament dryer.
Drying PETG with a Filament Dryer
A filament dryer, as the name also suggests, is a device designed specifically to dry spools of filament, and due to this, using one to dry your PETG will provide you with the best user experience among all the methods in our list.
Compared to the two methods we have mentioned so far, using a filament dryer is pretty straightforward in comparison, as all you will need to do is set the temperature to 55 degrees Celsius, set the timer to 6 hours (you can always repeat if 6 hours aren’t enough to remove all the moisture), pop your spool of PETG in, and let the filament dryer do the rest without having to worry about the time or the temperature stability.
While a high-quality filament dryer shouldn’t have any issues with temperature stability, it can still be a good idea to verify the temperature with an infrared thermometer before placing your filament inside for the very first time using the filament dryer, which will allow you to ensure that the device doesn’t have any defects.
Additionally, having a filament dryer at hand will come in especially handy if you’re living in a humid area where even the filament that’s in active use can be affected by moisture, as you can set it to a low temperature, such as 35 degrees Celsius, and keep it running until you need to use your PETG again, which will ensure that it stays moisture-free without being packed away for long-term storage.
Drying PETG with the Heated Bed
Finally, if you don’t have access to any of the devices we have mentioned so far, using the heated bed of your 3D printer can make it possible to dry your PETG, and even though this method both requires more effort and is less reliable at the same time, it can get the job done with a bit of extra work.
For this method, the first thing you will need to do is to find (or 3D print) an enclosure that will trap the heat of the print bed inside with your PETG while also having gaps for airflow, such as this 3D printable one.
Next, you will need to find a part (the design we have linked to earlier includes this part as well) that will allow you to elevate the spool of PETG and protect it from coming into direct contact with the heat of the print bed, as the surface of the print bed will be much hotter than the inside of the enclosure.
With that done, the following step is to find the bed temperature value that can provide a stable internal temperature of 55 degrees Celsius through trial and error (100 degrees Celsius should be a good starting point), as simply setting the bed temperature to 55 degrees Celsius will result in the internal temperature being much lower due to some of the heat being lost.
Once you verify the temperature inside with the help of an infrared thermometer, you can then place your spool of PETG inside the enclosure and on top of the part that elevates it, leave it in there for 6 hours at a time, test for moisture, and repeat until all the moisture is gone.
Storing PETG Filament Correctly to Keep It Moisture-Free
The best way to avoid ever having to dry your PETG filament is to keep it moisture-free from the beginning, which is entirely possible once you take the necessary steps to create an environment where your PETG cannot absorb any moisture no matter how long it stays there.
Below, you can find the various tips & tricks we recommend using to create a moisture-free environment for your spool of PETG, together with details that’ll help you set things up.
Place Your PETG In Airtight Containers
The very first thing you can do to store your spools of PETG in a moisture-free way is to place them in airtight containers, as this will largely prevent the moisture in the environment from making its way into the plastic by sealing it off and letting no air get inside.
Since the only thing that matters for our purposes is to prevent air from coming in, latching storage boxes, food containers, and basically any other container you can think of which comes with a mechanism that makes it airtight will do the job, regardless of size or shape (as long as you can fit the spool inside).
That being said, if you want to take things to the next level, you can also opt for a container that’s vacuum sealed (quite common with food containers nowadays), and while these containers are usually more expensive (especially the ones explicitly produced for storing filament), they’ll provide an extra layer of security that can come in especially handy in high-humidity areas.
Additionally, if you’ve already opened the filament’s packaging, it would also be a good idea to add another layer of protection by placing the spool in an airtight bag (such as a vacuum bag) before putting it in the container, which will practically bring your filament to the same state as an unopened one in terms of protection from moisture.
Bonus Tip: If you live in an area where humidity is high, which would also require you to keep the PETG you’re currently using in a dry box to prevent it from absorbing humidity, but don’t want to spend too much on a dry box, you can convert your airtight storage box into a dry box that can accommodate multiple spools of PETG at once with some DIY magic.
Throw In Desiccants (and Humidity Indicators) With Your PETG
To take your storage conditions a step further and practically make it highly unlikely for your PETG to get damp even in the slightest, you can throw in some desiccants in the airtight container (and bag) you’re storing your filament in, which will absorb any moisture that gets through before your PETG does due to its high hygroscopicity.
When it comes to desiccants, there are many options you can choose from, whether it’s the widely used silica gel, calcium chloride, or molecular sieves, with each option coming with strengths and weaknesses of its own.
Without going into too much detail, we can say that molecular sieves are the most effective when it comes to pulling humidity levels down to be as close to 0 as possible; but also the most expensive (can be reused); silica gel is the least effective (can be reused), and calcium chloride falls somewhere in the middle (can’t be reused).
While the choice practically comes down to how much humidity you’re dealing with, even silica gel, the least effective option among the three, should get the job done without issues in almost every case, which is why our recommendation would be to start out with the one that’s easiest to obtain, which will most likely be silica gel, and switch to one of the more effective options if it becomes necessary.
Additionally, while it won’t directly have an effect on the moisture levels of your PETG, throwing in a humidity indicator card alongside the desiccant is also a great idea, as it will allow you to find out if humidity is building up inside, whether due to a problem related to the airtight container, due to the desiccant becoming fully saturated, or due to the amount of desiccant not being enough to keep up with the moisture.
This way, you’ll be able to quickly intervene in a case where the humidity inside is about to get to a level that can affect your PETG negatively and take the necessary measures before the moisture actually starts getting into the filament.
Store Your PETG In a Cool & Low-Humidity Environment
Finally, while it goes without saying, storing your PETG in the coolest and least humid environment possible in your home is a simple but effective way to keep your filament as dry as possible, and combined with the two precautions we have talked about earlier, will ensure that you never have to worry about moisture in your PETG again.
Under ideal circumstances, the area you’re storing your PETG in should get sufficient airflow through windows and not be too close to the kitchen or bathrooms, which we can consider to be the most humid rooms in any home, with showers, sinks, dishwashers, and kettles all contributing to an increase in humidity.
Identifying PETG Filament That Has Absorbed Moisture
While it’s usually not possible to find out whether your spool of PETG filament has absorbed moisture by examining it, the signs that appear once you start printing with PETG that have absorbed moisture are pretty clear-cut and easy to notice.
Below, we have listed the most common signs you can come across when printing with a wet spool of PETG filament, which we highly recommend keeping an eye out for if you suspect your PETG has absorbed moisture.
Steam Comes Out of the Nozzle
One of the common signs of printing with PETG that have absorbed moisture is steam coming out of the nozzle at particular points of the print where the parts of the filament that have a high moisture concentration are being melted.
Since the moisture inside the plastic, just as the plastic itself, gets exposed to the high temperatures of the hotend, it turns into steam as soon as it’s released and escapes out of the nozzle in a very noticeable way, practically confirming that your spool of PETG has absorbed moisture.
Nozzle Makes Popping & Cracking Sounds
Another sign of printing with a moist spool of PETG is the nozzle making popping and cracking sounds, usually in random intervals, due to moisture not being evenly distributed throughout the spool.
Similar to when steam comes out of the nozzle, the popping and cracking sounds also occur when the portions of the filament that have absorbed moisture come into contact with the heat bloc, and if you pay attention to the nozzle when you hear these sounds, you’ll most likely notice that steam is coming out as well.
Extrusion Is Inconsistent
While it can be harder to observe than the two signs we have talked about so far, at least until your 3D printer completes the print or finishes a large portion of it (unless it happens on the first few layers), inconsistent extrusion is one of the trademark signs of printing with a moist spool of PETG filament.
Whether it’s due to your PETG getting brittle as a result of the moisture absorption, the moisture causing the filament to melt in an uneven way, the vaporization of the water throwing off the nozzle pressure, or the water that has turned into steam forming bubbles inside the filament, inconsistencies in extrusion, in this case, usually present themselves in the form of missing plastic, such as parts of the layers being thinner than the rest, or the print surface having noticeable gaps in some areas.
Printed Surfaces Look Fuzzy
Yet another sign of printing with moist PETG is the surface of your prints looking fuzzy, with plastic “hairs” that look similar to stringing but are usually shorter and randomly scattered throughout the surface.
In this case, the issue stems from the absorbed moisture turning into steam as the hotend melts the affected parts of the filament, with the steam build-up in the nozzle causing a sudden increase in pressure that ends up with the plastic uncontrollably oozing out of the nozzle and causing the appearance of the fuzz.
Bubbles (Air Gaps) & Holes Appear on the Surface
Another common sign you can come across when printing with moist PETG is the appearance of bubbles and holes on the surface of your prints, which will drastically reduce the print’s visual quality.
The issue, in this case, is a result of the 3D printer under-extruding as a result of factors such as inconsistencies in melting due to parts of the plastic being affected by moisture and steam pockets that appear as a result of moist filament getting heated, which causes the layers to receive less material than they actually should in particular areas.
Layer Adhesion Is Poor
Poor layer adhesion is yet another consequence of printing with a spool of PETG that has absorbed moisture, and even though it may not be possible to observe it as easily as the rest of the signs here unless it’s severe and leads to layer separation, it’s a sign to watch out for.
Similar to the appearance of air gaps and holes, poor layer adhesion also stems from under-extrusion in this case, as layers not getting sufficient material due to moisture adversely affecting the extrusion prevents them from forming bonds that are strong enough with each other to provide enough strength to the printed part.
Stringing
Last but not least, stringing, a problem that we’re all familiar with, can also stem from using a wet spool of PETG, and while there are so many other reasons that can also cause stringing, moisture is a factor we definitely have to keep in mind.
Similar to prints becoming fuzzy, stringing is also caused by the filament flowing out of the nozzle in an uncontrollable manner due to the nozzle pressure inconsistencies that occur as a result of the moisture in the plastic evaporating and turning into steam.
Conclusion
While printing with a wet spool of PETG filament will most likely lead to print failure or a severe loss of print quality in the best-case scenario, finding out that your PETG has absorbed moisture, drying it, and storing it in a way that’ll keep it moisture-free from now on shouldn’t be too challenging of a task once you know what to do.
Finally, if you have a spool of PETG that has been around for a while; and you’re unsure whether it has absorbed moisture or not, we highly recommend applying the drying process regardless before trying to print with it, as this will ensure that you don’t face any issues down the road if the PETG was indeed wet, and save you from the trouble of dealing with a failed print.
As a software developer by profession, David has been particularly interested in how 3D printing works even before he picked up his first 3D printer, and completely fell in love with the hobby once he got his hands on a Prusa i3 MK2 for the first time back in 2017. Due to him enjoying both the functional and the non-functional sides of 3D printing equally, you’ll rarely see David’s 3D printer in an idle state.