As you may already know, keeping PETG filament in a plastic bag or even in a cardboard box is not a good idea as it doesn't protect against moisture for long period of time.
This blog post will answer two key questions:
1. Why is moisture so bad?
2. What is the best way to keep your filament dry?
1. Why moisture is so bad
PETG filament has a tendency to absorb atmospheric moisture which can cause hydrolytic degradation during processing. This results in a decrease in molecular weight of the resin and in a reduction of the physical properties of the final product.
According to manufacturer specification, in order to avoid this degradation PETG filament should be sufficiently dried to a moisture level of less than 600 parts per million (ppm) before processing.
We've done the science, so lets review our practical test to see why moisture is so bad. We created 3 samples using a regular 3D printer (Creality Ender 3) and 0.8mm nozzle to demonstrate this.
Sample 1 - no moisture control: PETG filament sat on a shelf in the basement for couple of days outside of the bag (summer time and around 59% humidity level). We loaded this PETG filament into the printer, heated the nozzle to 230°C, and then extruded 100mm of filament wire and cut.
Sample 2 - partial moisture control: The remaining spool from Sample 1 was then placed into a plastic container heated to 50°C for 3-4h (filament dryer box). We then extruded another 100mm of filament wire and cut.
Sample 3 - full moisture control: The remaining spool from Sample 2 was then placed into a sealed plastic container with 1kg desiccant bag for 12-24h. We then extruded another 100mm of filament wire and cut.
Now we have 3 extruded filament wires for comparison. Sample 1 is on top, Sample 2 is in middle, Sample 3 is at bottom.
2. How to keep filament dry
One of the best ways to keep filament dry is by using the right storage container and an appropriate quantity of desiccant. Pick a contained that can create a good air seal. Plastic bins and buckets with lids work well for this. Do not use containers such as cardboard boxes or plastic bags as they cannot be sealed well. Next, use 1 - 2 kg of desiccant to actively remove moisture from the filament.
To get this quantity of desiccant you can either purchase it or collect it overtime from shipping bags or other products that include them. In order to regenerate the desiccant (i.e. remove moisture it accumulated), bake it in the oven overnight at 115°C (240F) for 10-12h. If you are looking for more specific instructions, there are lots of YouTube videos describing how to do it. After the baking is completed, place the dried desiccant into breathable bags (cotton is a good option), measure the weight, and write it on the bag using a permanent marker. This will be used to monitor the time for the next regeneration cycle. Place 1-2kg of desiccant (depends on the container size) into each container with filament. This should be enough to keep the filament dry for up to a year. We suggest measuring the weight every month and if it is 5-10% greater than your starting weight then its time for the next regeneration cycle.
Please note the humidity level inside and outside container. The difference speaks by itself.
This bucket with lid set-up works better than a bin because it has a better seal. As a result, desiccant recovery can be done less frequently.
I hope our explanation will convince you to keep filament dry to get the best possible result out of your materials.