Drying PETG: 6 Ways To Treat Wet Filament

PETG is a hygroscopic type of filament. It absorbs moisture from the environment like a sponge, and it’ll likely need drying before printing, even if you’ve stored it properly.

Drying PETG is traditionally done in a filament dryer or an oven. You can also use a food dehydrator, which works similarly to a filament dryer. Alternatively, you could dry PETG in a vacuum chamber, even though the method is not as effective as drying with heat.

How To Dry PETG Filament

The traditional method of drying PETG – as well as other types of hygroscopic filaments – is in a filament dryer or kitchen oven.

Vacuum chambers are also available for this purpose. They are cheaper than specialized dryers but not as effective.

1. Filament Dryer

Filament dryers are specialized appliances designed specifically for the purpose. They vary in design from small boxes that can hold one or two spools to larger devices similar to food dehydrators. 

Regardless of its size, a filament dryer’s main advantage is the possibility of using pre-programmed settings for the type of filament you want to dry.

Most of these devices can also be used for storing filament after printing, controlling the internal temperature and humidity to prevent moisture absorption. 

To dry the filament using this method: 

1. Unwrap the spool if necessary and place it in the filament dryer.
2. Scroll through the options until you find PETG. This option will set the right temperature and dry time automatically. A beep will let you know when the filament is ready to use.
3. Alternatively, if the unit you use doesn’t have a pre-programmed setting for PETG, set the temperature to 65°C (149°F) and let the filament dry for about six hours.

2. Kitchen Oven

Convection ovens work in about the same way as specialized spool dryers do. They circulate hot air around the spool, eliminating moisture through evaporation. 

The main downside of drying filament in a kitchen oven is that the appliance might not be perfectly calibrated. 

This means that it could heat up higher or lower than the set temperature.

Another downside is the absence of moisture control. While spool dryers can detect the amount of moisture in the spool and signal you when the filament is ready to use, your good old oven can’t do that.

Thus, you’ll have to rely on other methods to determine the wetness of your filament. 

Despite these downsides, the oven can be an easy solution if you don’t have a specialized dryer and don’t want to buy one.

To dry PETG in the oven: 

1. Set the oven to 65°C (149°F) and wait for about half an hour. This should give the appliance enough time to reach and stabilize the temperature. 
2. Measure the exact temperature in the oven with a good thermometer. This step is crucial to ensure the oven isn’t over- or under-heated. 
3. Place the spool in the oven for at least six hours. It is preferable to check the temperature regularly during this time to avoid overheating. 

To test if the filament is dry, load it into the printer and observe extrusion.

If bubbles form in the extruded material, the filament is still wet and needs longer drying. A hissing sound also signals wet filament whether or not you see bubbles.

3. Food Dehydrator 

A food dehydrator comes as a low-cost alternative to a large-capacity filament dryer if you want to treat more than two spools at a time. 

Food dehydrators use the same principle as the oven or filament dryer (hot air circulated around the material) and can have the same downsides as a kitchen oven. They might not be perfectly calibrated, and they won’t tell you when the filament is dry. 

To dry the filament in a food dehydrator, set the temperature and let the filament dry for four to eight hours. 

The PETG drying temperature and time can vary when drying filament in the dehydrator, giving you the possibility to treat various materials at the same time. 

• Set the dehydrator to 149°F (65°C) to dry PETG and PLA at the same time
• Set the dehydrator to 158°C (70°C) to dry PETG and polycarbonate at the same time. 

4. Vacuum Chamber 

The three methods above are the traditional ways to dry 3D printing filament. A newer method involves drying the filament in a vacuum filament dryer. 

Also called a vacuum chamber, this machine eliminates moisture by lowering the air pressure. 

The lower pressure changes the boiling point of water, speeding evaporation when a minimal amount of heat is applied.

In theory, vacuum drying could prevent changing the characteristics of the filament. However, the method is not as effective as heat drying because the moisture tends to be reabsorbed into the filament quickly once the pressure returns. 

Adding desiccant to the vacuum chamber could help solve the problem, but the filament might still retain more moisture compared to the traditional drying methods.

To dry PETG in a vacuum filament dryer, set the spool in the chamber, add desiccant, and let the machine do its job for three to four hours. 

5. Dry On Heated Bed

Sometimes, you might have to dry filament without relying on an oven, food dehydrator, or spool dryer. 

This might happen, for instance, if you’re setting up a 3D printing shop and only have the printer and some spools on site. 

In such an instance, you could take advantage of your printer’s build plate to dry the filament. 

For this method, you need a cardboard box or aluminum foil. 

1. Turn on the printer and heat the build plate to 65°C. 
2. Place the spool in the middle of the plate and cover it with the cardboard box or aluminum foil. 
3. Poke some holes in the box or foil to ensure air circulation. 

Let the filament dry for at least eight hours. 

Due to poor air circulation, PETG can take much longer to dry on the printer bed compared to all other methods. Using a fan heater that blows air right onto the cardboard should help speed out the process.

6. Dry PETG In Freezer

A functional albeit unusual method of drying PETG filament is keeping the spool in the freezer for some time. 

This method doesn’t work with other filament types due to their chemical composition. With PETG, the moisture absorbed by the filament evaporates through a process called sublimation.

Even though the method works, dehydrating the filament in the freezer can take a lot of time – typically a week or more. So, you should only try this method if you don’t mind waiting.

Alternatively, you could store the spools in the freezer, preferably in sealed bags. 

It is also crucial for the PETG to go through a gradual thawing process before using it. 

Condensation build-up is one of the main issues when taking the spool out of the freezer, as some of the moisture is usually absorbed by the material. 

To prevent it, you should rise the freezer’s temperature gradually until its highest setting. Then, move the spool in the fridge set on the lowest temperature and raise it gradually until you get to the highest setting. 

At this point, it should be safe to bring the spool out and let it reach room temperature before loading it onto the printer.

---

Factors That Affect PETG Drying Rate

All drying methods require four to eight hours at least to dry out the filament.

But how long does it take to dry PETG filament? That depends on a variety of factors.

Moisture Level 

The main factor that can affect PETG’s drying rate is the level of moisture in the filament. 

PETG is a highly hygroscopic material that absorbs water from the environment even when stored correctly. The only way to store this filament without worrying about moisture absorption is by keeping it in a filament dryer at all times. 

However, running a filament dryer continuously can have an impact on your energy bill.

To minimize moisture retention, you should place the spool in a vacuum bag, suck out the air, and store it in a filament box. PETG filament stored correctly can be dried in four or fewer hours. 

If you’ve stored the filament on a shelf or in a box with desiccant but without sealing it in a vacuum bag, you should let it dry for at least six to eight hours. 

Dry Method Used 

The way you dry PETG filament can also influence the drying rate. 

Drying the filament in a vacuum chamber is the fastest method, but only if you add desiccant. PETG is usually ready to use in about four hours.

However, vacuum chambers aren’t generally capable of removing all moisture regardless of how long you let the spool dry.

The freezer method is the lengthiest, requiring leaving the filament in the freezer for at least one week. 

Drying PETG in a ventilated oven or a specialized filament dryer provides the best results/dry time balance.

The table below shows how fast your filament is likely to dry*: 

Method	Average Drying Time
Filament dryer	4-6 hours
Ventilated oven	4-6 hours
Static oven	6-8 hours
Food dehydrator	6-8 hours
Vacuum chamber	3-4 hours
On build plate	8-12 hours
In freezer	At least 1 week

*These are averages obtained through independent tests and are intended to use as a reference only. The actual dry times may vary depending on the PETG brand and how much moisture your filament has retained during storage.

Ventilation 

Air circulation is essential to speed up the drying process, so the presence or absence of ventilation will affect the drying rate.

As a rule of thumb, filament dries faster in ventilated environments. The only thing to pay attention to is the temperature of the air if you’re using an external fan.

Always blow hot air on the spool, or the temperature difference may lead to some condensation.

Filament Age

Surprisingly, filament age is another factor that determines how fast PETG can dry. New filament typically dries faster than old one.

---

Importance Of Keeping PETG Dry

Finding the right method to dry out PETG shouldn’t be complicated, but keeping the spool dry during storage is equally important.

• Moisture can damage PETG filament kept in storage, turning it brittle
• Objects printed out of wet PETG usually deform during the printing process
• Printing with wet filament could damage your printer due to the steam created as moisture evaporates
• Filament may become more prone to stringing and have a slightly bleached color 
• Objects may have a different texture when printing with wet filament

---

Frequently Asked Questions

Is it safe to dry filament in the oven?

Drying PETG and other types of 3D printing filaments in the oven is perfectly safe as long as the temperature of the oven doesn’t exceed the filament’s melting temperature.

The ideal drying temperature for PETG is 60°C to 70°C, and it is usually recommended to keep the oven at 65°C (149°F). 

How to tell if PETG is still wet?

One of the easiest ways of telling if the filament is still wet is by printing a mock object. 

Signs of a wet filament include: 

• Bubbles forming on the extruded filament 
• A hissing or crackling sound while the filament is extruded
• Abnormal stringing or oozing
• Uneven extrusion lines 
• Uncharacteristically textured surfaces or fuzzy printed surfaces caused by severe stringing
• Poor layer adhesion and severely reduced part strength
• Delamination of printed object

Does PETG absorb moisture after printing?

PETG is a hygroscopic material, and it remains so even after printing.

The filament keeps absorbing moisture after the printing process, and this could sometimes lead to mold growth on PETG objects when stored in particularly wet environments. 

However, the integrity of PETG objects won’t degrade and can remain watertight if printed correctly, even if the material absorbs some moisture. 

---

Conclusion

PETG is a highly hygroscopic material that can absorb moisture from the environment in a very short time. Storing it in watertight and airtight bags and drying the filament before printing is crucial to guarantee the success of your project. 

Drying the PETG in a filament dryer or ventilated oven will yield the best results. Alternatively, we hope this guide can help you choose the method that best suits you.