Yeah I know, it sounds like Nature Preservation, Ecology, Greta Turnberg, etc.
Nope, nobody protesting here.
Filament, with small exceptions, is a polymer, which is simply put a combo of monomers, at least two in each combination. If less than two, than no more poly...
Plastic, yup, not all that plastic is Nylon, some is Starch, like PLA, basically potatoes or maize.
And many others, but have something in common with each other, they absorb humidity, that is how they become impermeable, once saturated, nothing else goes through.
And that is good, with exceptions.
The main exception that hurts you is when you print it, you see, in printing you need some 200 Celsius, minimum, some filaments require 300 Celsius, but water... at 100 vaporizes.
So what, let it go. OK, but before that; remember, it is trapped in every small nano porosity of your filament.
What happens if you put a metal pot on the stove, fill it with water than silicone the lid around and let it boil? Right, it blows the lid away. Water turning into vapors grows in volume, exponentially. That pot with sealed lid is but one of your gazillion of nano porosity-es in your filament.
Hence you will note at the exit of your hot end nozzle the filament popping like popcorn in the microwave oven, with the consequent reduction in end product visual integrity, aspect and resistance, briefly put, you ruined your print.
OK, simple solution, do not put the filament in water, easy. Not that easy.
Water is like love, and remember, love is in the air... everywhere. So does water. And on the principle of communicating vases, every single nano porosity in your filament will fill up to balance the imbalance. There you have it.
I have seen a lot of DIY solution tried them all, not good, putting the filament in a bag with a silica pellets absorbing bath, only works until the silica drinks water to capacity, later on is the filament turn, and if filament is already compromised will release zero to the silica pelts.
Solution two, put the filament in a bag of dried rice. Saw no improvement this way either.
So I took it to the science, science tells me if I want to eliminate water in the filament first I must evaporate it without vaporizing it.
According to filaments, PLA 50 Celsius ABS 60 Celsius, Nylon 80 Celsius, for several hours, minimum 5, does the job.
And it bloody does it, but how?
How do you keep a constant temperature for 5 to 10 hours?
Microwave oven? nope, it melts your filament (no perfectly stable temperature),
OK induction oven... nada, melts the filament sooner or later,
regular gas oven, not even close,
any oven, nope, none.
You see, those ovens were intended for cooking, so temp going up or down by 30 Celsius is no problem in them ovens, but it is for your filament, you have no idea how nice it is to pull a baked filament out of oven just to see that all the wire is glued to itself.
Hence I dug for a hot printing bed, put it in a box, tied it to an Arduino, set the temperature for the printing bed at 50, let the filament in the box a few hours, and... voila.
Worked, I can print with dry filament now.
Than I found out some Chinese company already makes them dryers not only with precise temperature sting and control, but also timer and also a.... tada.... scale, yup, and electronic scale so you know all the time how much filament is left in the spool while you print, because yes, there is some small rollers on the bottom so your spool spins freely to feed the extruder too. You can buy them on EBay, Amazon, etc.
OK, I have dried my spool, printed something, and now back on shelf, but... it will suck water again, from the atmosphere, and we all know that in between 2 projects a filament my wait months on a shelf. Than I have to bake it again 5 to 10 hours so I can print. Or maybe not.
Hence I bought a large food sealing bag roll, the filament spool fits in alright, and I bought a food vacuum sealer machine for 30 bucks on Amazon or Ebay or ... can't remember.
Science told me in my dreams that if atmospheric water humidity never reaches the filament, my spool will stay dry. ( I have those night things called visions, when Science talks to me, but takes no talk back... Gee I am a prophet, nearly, they could talk back.)
So if I place my spool of dried filament in the vacuum machine, suck all the air out (humidity included) chances are it will stay dry as long as the bag is sealed and the air stays out.
Did so, kept a few rolls for a year (yes I am that patient) than tried them now, no silica or other silly stuff with them in the bag, just lack of air, and it worked like a marvel.
SO, to conclude; dry it up (not melt it down), vacuum store it well sealed, and it does the job.
I love science.