Does PETG Need to Be Dried? All You Need to Know

It’s a good habit to dry 3d printer filaments before putting them into work. Some filament materials are more sensitive to moisture, and some are less affected by it. In my experience, PETG is in the middle of this spectrum. So:

Does PETG need to be dried? It depends on the following parameters:

• ambient relative humidity (Percentage of the relative humidity of where you store the filaments or simply where you live if they are not in a sealed space)
• your desired print quality
• mechanical properties, such as tensile strength.

Now let’s talk in more detail. How much relative humidity is acceptable? And how it changes your print quality? Keep reading!

How do I know if my PETG filaments are wet?

The first and most effective way to know if your filament is wet is to listen to the extruder sounds. If you hear a noise like popping and cracking, it’s mostly because of wet filaments. The next sign is the random bubbles inside the melted filament after it leaves the nozzle. These are the obvious signs of wet filaments.

However, if the moisture level is low, It may only affect the printing quality by stringing, oozing, and rough edges. For example, if you live in a place with a relative humidity lower than 30% and you put your PETG filament spools in a room, you may only see more stringing without extra bubbles or a noisy nozzle. So, low humidity won’t affect the printing quality that much.

How humidity affects quality?

In theory, every polymer absorbs moisture at some levels. Some polymer filaments tend to absorb water, and they are called hydrophilic polymers. Hydrophobic materials are the opposite. However, filament materials like PVA, TPU, and especially Nylon have more tendency to absorb water and, unfortunately, ruin your piece.

Depending on the amount of absorbed water, humidity can cause different problems at different levels. The least problem you can face is to have more stringing around edges and corners. Surface quality may fall, and the smooth areas become rough. However, a little moisture won’t create bubbles and popping sounds, and mechanical property changes will be minor.

As the filament absorbs more moisture, all the bubbling, cracking and extruder sounds become more visible. As the absorbed liquid water goes into the hot end, it warms up and becomes steam, causing extruder noises and filament bubbles. As the filaments absorb more water, they make more strings.

As a general rule, wet filaments have less strength, so they break easily. Their impact resistance will decrease because the H2O molecules weaken the polymer bonds and lower their resistance forces. So if your final part should withstand force or torque, your PETG filaments need to be dried.

PETG doesn’t absorb too much water; Especially if you keep them in a low humidity place, there won’t be severe changes. As a rule of thumb, if the relative humidity is around 30% or less, there is no need to dry PETG. For example, if you live in Nevada, Arizona, New Mexico, or Colorado, the humidity level is ok.

However, it is highly recommended to dry other materials like Nylon. So drying filament is a good skill to have as long as you use hydrophilic filaments.

How to dry PETG and how to keep it dry?

There are some easy ways to do it. One option is to use a filament dryer. Filament dryers are specifically designed to dry 3d printer filaments. These devices dry filaments with different methods; They usually heat the filaments a bit and dry them in a few hours.  Some dryers have small holes and allow the filament to pass and go to a Bowden tube and stay dry as the print goes on. However, they are expensive and mostly used by professionals.

The easiest option is to use an oven! All you need to do is just put the filament spools into the oven, set the temperature, and wait a few hours. The more you leave the filaments, the more they dry. This method has some cons.

The oven’s temperature is usually not accurate enough, and there is a possibility of fusing the entire spool. If the oven gets overheated, the filaments may pass their glass transition temperature, and release gas, so always use a margin of safety when drying with your oven. I personally don’t like to put hot plastics where I cook my food!

The last and best option is to use a food dehydrator. They are designed for drying fruits, but they use the same temperature range to dry fruit as we use to dry filaments! So they provide more accurate temperatures than ovens. You can get a food dehydrator for under 40$ and use it for drying filament.

They usually have meshing and removal layers that can be changed to fit one or more filament spools. Keep in mind that you need to check their interior dimensions and see if they have enough space for filament spools.

Now let’s assume you pick a food dehydrator. How much time does PETG need to be dried? And what is the best temperature for drying it? PETG should be dried at a temperature of around 65 ^oC for more than four hours. However, you can use a temperature of less than 65 ^oC with more time.

The filament temperature should never go above its glass transition temperature, and the glass transition temperature for PETG is 88 ^oC. After that, the filament will start deforming. After drying some filament spools, you can put them into sealed plastic bags or boxes to keep them dry.

Conclusion

It is a good idea to dry PETG filaments if you store them in a humid environment. The less water they contain, the better the printing quality will be. Drying filaments don’t cost too much, and it’s easy to do. Even if the PETG filaments are not sensitive to low humidity, drying them is worth the effort.