Is PETG Hygroscopic (Does It Absorb Water)?

Hygroscopicity is a solid material’s capability of absorbing water from the environment, which also determines how likely a material is to react to moisture in the air.

Since the likelihood of a 3D printing filament absorbing moisture is a vital factor to keep in mind due to the negative impact of dampness on the printing process – hygroscopicity of the material plays a significant role in the storage and maintenance of filaments.

Today, we will be talking about the hygroscopicity of PETG in particular, as there is a lot of confusion about the relationship between water and PETG in terms of water resistance and moisture absorption.

So, is PETG hygroscopic, or in other words, does it absorb water?

PETG is indeed hygroscopic, meaning that it’s prone to absorbing water from the environment and retaining it.

As hygroscopic materials can easily absorb the moisture from the air, a spool of PETG filament that you store in a humid environment will eventually become wet.

Next up, we will take a more detailed look at how PETG being hygroscopic can impact the printing process, discuss the water-resistance capabilities of PETG, and find out how you can check your PETG for signs of wetness.

Is PETG Hygroscopic (Does It Absorb Water)?

Hygroscopicity of PETG is a factor that primarily concerns the storage process, as a spool of filament is most likely to absorb water through the moisture in the air while it’s in storage.

As PETG is a hygroscopic material, it does absorb and retain the water in the environment.

In most cases, PETG filaments unnoticeably become wet by absorbing the moisture in the air due to improper storage conditions where they are exposed to humidity for prolonged periods.

While moisture itself doesn’t necessarily damage the filament, the problem arises from the combination of heat and humidity in the case of the 3D printing process.

When the moisture in the filament and the heat from the nozzle come together, the filament starts expanding due to water exiting it (turning to steam), which distorts the printing process in the form of inconsistent extrusion, weak layers, and suboptimal print quality (such as hairy prints and stringing).

That being said, even though the hygroscopic nature of PETG is indeed a disadvantage for the purposes of 3D printing, keeping PETG moisture-free or drying it before the printing process isn’t the most challenging task.

Is PETG Water Resistant?

Even though hygroscopicity and water resistance sounds like they should be at two different ends of the same spectrum, the situation contradicts what intuition tells us.

While PETG does indeed absorb water, it’s also highly water-resistant at the same time, allowing you to print waterproof models with your 3D printer.

Since absorbing water doesn’t damage the structural integrity of PETG, the hygroscopic property poses no threat to its water-resistance capabilities.

In fact, PETG is usually the best choice for printing a waterproof model in most cases due to the fact that it’s much more accessible and undemanding to print compared to alternatives such as ABS that don’t offer anything extra in the front of water resistance.

How Can PETG Be Water Resistant and Hygroscopic?

The fact that PETG is both water-resistant and hygroscopic at the same time has a simple explanation despite the fact that a material that absorbs water being water-resistant sounds unintuitive at first.

To understand how PETG can be both water-resistant and hygroscopic, let’s start by looking at the definition of both of these terms.

Water resistance, or waterproofness, refers to the fact that water does not negatively affect the material in some way, such as causing it to dissolve or deform when it comes into contact with the part.

On the other hand, hygroscopicity is the capability of a solid material to absorb the water in the environment and retain it.

By combining these two definitions, we can explain how PETG is hygroscopic and water-resistant at the same time.

While PETG does absorb water due to its hygroscopic property, the water it has absorbed, or any water it comes into contact with, does not damage its structural integrity.

As a result, even though a model printed with PETG may become wet due to the moisture in the air, the wetness won’t degrade the model in any shape or form.

With this in mind, we can conclude that a material can be both hygroscopic and water-resistant at the same time without problems.

How to Know if PETG Filament Is Wet?

As wet filament can completely ruin the printing process, knowing the signs that a wet spool of PETG filament will display is a handy piece of information to have.

Since it’s not quite possible to tell whether PETG is wet or not before you actually print with it, here are the signs you should look out for during the printing process if you suspect that your filament is wet:

  • Unusual sounds during print – For the most part, these sounds present themselves in the form of hissing and popping.
  • Steam coming out of the nozzle – As the water in the PETG evaporates due to the heat, you should be able to see the steam produced as a result.
  • Adhesion issues – The moisture in the filament can cause adhesion issues between layers, preventing layers from correctly bonding to each other.
  • Inconsistencies in extrusion – While the most common sign is print lines varying in size, you should also be on the lookout for issues such as stringing and fuzziness on the print surface.

Wrapping Up

As moisture affects filaments negatively by causing issues during the printing process, hygroscopicity is one of the most vital pieces of information that you should know about the filament you buy.

To quickly recap, PETG is a hygroscopic material, meaning that a spool of PETG filament can absorb the water in the environment, including the moisture in the air.

That being said, PETG is also highly water-resistant. Despite sounding unintuitive, water-resistance and hygroscopicity aren’t necessarily mutually exclusive.

A vital point to keep in mind is that the hygroscopic nature of PETG requires it to be stored appropriately, as a moist spool of PETG filament can easily ruin the printing process with the problems the moisture brings.

Happy printing!