My notes regarding Fused Filament Fabrication (FFF) / Fused Deposition Modelling (FDM™) additive manufacturing (or “3D printing”) on my Prusa MINI+.
Most informative take I've seen on this, from the page comments on Beat Moisture Before It Kills Your 3D Printing Filament - MatterHackers:
I would assert that since “drying” filament never requires heat in the range of water's boiling point, that all filament drying depends ENTIRELY on the RH of the surrounding air. Raising the temperature is simply a convenient way to lower the RH of the surrounding air to such a low value that excess moisture in the filament will move to the air. The air acts as a desiccant! This also happens in a freezer where varying temperature causes condensation onto cooling coils followed by periods of VERY low humidity thus extracting moisture from the filament if it has more than the circulating air.
If I put a roll of dry filament and a humidistat into a mostly evacuated (clear or at least translucent) airtight bag, after some time (say an hour) the humidistat should register the humidity where the air and filament are at equilibrium for the current temperature. THIS TELLS ME, for a given temperature, the RH above which the filament will absorb water and below which it will give up moisture.
If I put that same humidistat in a bag with dry desiccant at the same temperature and it doesn't read lower than the dry filament then adding the desiccant to the filament bag will ADD humidity to the filament. But, provided it IS lower, it WILL REMOVE HUMIDITY from the filament until the equilibrium point is reached. I think that people who say you can't dry filament with desiccant simply don't utilize a ratio of dry desiccant to filament necessary to do the job.
If your oven can't be set low enough to avoid harming your filament you CAN use desiccant to dry it. You just need a lot (like 1kg or more) and you may need to dry the desiccant more than once. But drying desiccant is far easier because it withstands boiling temperatures ( 212°f - 100°c) and dries faster.
Personally, I keep each of my open filaments on a stand inside a separate zip-lock bag with color changing desiccant. I put a small hole in the bottom of the bag and feed the filament out the hole so it never leaves the bag, even while printing. I just put a small piece of tape over the hole if I switch filaments. Once a bag has been taped once, I put a hole in the tape use the spool the 2nd time. If I need to re-seal it, the 2nd piece of tape peels of the 1st piece very easily and so the 2nd piece can be used to re-seal the bag many times. In fact it might last several spools before looing it's stick.
— Rick October 30th, 2021 at 8:09PM