Whether you are a 3D printing expert or a beginner, we are sure that you have already come across the worst nightmare of all printers: humidity in 3D printing filaments.

The ability or inability of a polymer to absorb moisture from the surrounding environment is called hygroscopicity and is a common characteristic of many types of materials, not just plastics. The causes of this phenomenon are to be found in the chemical characteristics of plastics.

The most common materials affected by this phenomenon are:

• PLA (polylactic acid)
• Nylon
• PVA (polyvinyl alcohol)
• TPU (thermoplastic polyurethane)
• PETG (glycol polyester)

The most common problems caused by humidity in filaments for 3D printing are:

• Brittle filament: Humidity can make your filament extremely brittle, this typically happens with PLA. You will notice that a filament from a newly opened PLA spool bends without any problems, but after a few months left on the shelf, the same filament breaks as soon as you bend it slightly. This is a symptom of PLA that has absorbed moisture. However, this does not apply to all polymers; for example, Nylon becomes more flexible if it has absorbed moisture.
• Filament popping: When a filament has absorbed moisture, it is easy to hear a popping sound when it is extruded from the nozzle of the 3D printer. This is because the water trapped inside the filament turns into steam due to the heat from the nozzle.
• Stringing: You will notice that with a humid filament, the dreaded stringing phenomenon tends to worsen.
• Rough surface of the piece: Another direct consequence of humid filament is that the same bubbles that form after the extruder will then be found on the finished piece, resulting in a very poor quality surface finish. The real problem is that the same roughness is also found between the layers, so the mechanical qualities of the piece will be compromised.

Stringing. Photo credit: Prusa

The Problem of Humidity in Filament Extrusion

Up to this point, we have analysed the issues of humidity when 3D printing and you are probably wondering: does humidity also affect the process of extrusion for creating new filament?

You bet it does!

Humidity is one of the main factors that could ruin your new filament. Think about the problem of filament that pops when it comes out of the printer nozzle, which usually has a diameter of 0.4mm. Now imagine the same problem with a 2.6mm nozzle, if the polymer (pellet or ground) has absorbed moisture, the entire filament will pop and be full of bubbles. These will also carry with them all the other problems found when printing: weak filament, very poor dimensional stability.

You must then consider that the material in pellet or ground form will absorb moisture much more easily and quickly than a spool of filament. The reason is that the pellet, but even more so your ground scraps, have a much larger surface area exposed to the air than the filament, making it much easier for them to be affected by humidity.

How can I dry plastic?

Household oven: Please refrain from doing so. Mixing the plastic you want to recycle with the cake you want to eat is never a good idea in any situation. Additionally, household ovens are designed to operate at high temperatures, so controlling low temperatures around 60°C is not very accurate. They often exceed the set temperatures by a considerable margin.

Laboratory oven: If you use our products for research, you probably already have access to a small laboratory oven. This is a good solution for drying polymers.

Food dehydrator: There are numerous food dehydrators available on the market that may suit your needs. Food dehydration occurs at relatively low temperatures for extended periods of time, which is exactly what we need. These products are designed to have low energy consumption and there are many affordable options available.

Spool dryer: If you use our products, you are likely a large-scale printer, and if you’re a large-scale printer, you probably already own at least one spool dryer, but you may not have known that you can also use it to dry extrusion material. The most common and affordable models reach temperatures of up to 60/65°C and allow for drying only PLA and PETG, but these are still the two most commonly used materials in 3D printing and likely the ones you’ll have the most scraps of.