I’m working on a humidity control environment for storing filament. I have a storage solution which is containers with silica gel inside. My question is what is the ideal humidity to store filament at.
I’d say below 60% for common filaments would be best. I think most dry boxes with silica get around 40%, which is ample for PLA and ABS.
I’m interested in what the others say. I keep my filament in Ikea bags with dessicant of varying ages, and I’ve only just received some humidity meters to put in them. In the few days since, they’ve not moved by more than 3%, and they’re all in the range 40% to 50%. It’s about 55% in the room.
@Deaths_Klown PLA absorbs moisture pretty well too. All my filament got ruined after half a year sitting out. Also there are more hydroscopic ones like nylon and PVA which should have more proper dry boxes to keep them as low as possible.
Ziplocks are PERMEABLE TO MOISTURE. It’s just a few mils of plastic. If water can get into your 1.75mm filament, it can get through a thin plastic bag. The bag slows it down, but doesn’t stop it. Same with shipping bags. The desiccant is likely expended by the time you open the bag.
You really need a thick polypropylene box with a gasket to keep moisture out long-term. PP is the only plastic that is nearly impermeable. And then you still need bone-dry desiccant if you want stray moisture to go into the desiccant and not the plastic filament.
Nylon or polycarbonate: dehydrate with heat before storing, and put in a drybox with calcium chloride (eg damp-rid) because nylon and PC are stronger moisture absorbers than silica. They will actually pull moisture out of used silica! You want <5% RH. As dry as you can get it. Or just dry before every print…
PLA: ~45% RH is probably ok, below 35% is better. People living in dryish places don’t need dryboxes. (I do need them in Houston.) A lot of what people blame on moisture (like filament brittleness) is actually aging of the crystal structure… highly-stressed PLA gets more brittle over time as the polymer molecules realign themselves, and filament has a lot of strain locked into it during manufacture as they draw it down to the proper diameter while cooling. Annealing with heat changes the crystal structure and fixes the brittleness, so people think drying fixed the problem when it was actually something a lot more complex. PLA wetness means steam and bubbles/popping, while brittleness is largely an age thing.
ABS: try to keep below 20% but the exact value isn’t too important. Indicating silica is fine.
PETG: you can often get away with not drying, but moisture makes the prints weaker and more brittle. Dry PETG makes stronger prints. The target RH will depend on the blend (they vary a lot by manufacturer) but I would think <20% RH should be a good target. Indicating silica is fine.
@Deaths_Klown dunno about anyone else, but I have a ton of colors and materials I rarely use but want on hand. Some of my PLA spools are 2-3 years old now. I churn through black PLA/PHA or silver ABS at a good clip, but purple PLA is like… special request only.
@Deaths_Klown Judge much? Not everybody is in your exact situation. I’m perfectly happy to spend ~$100/year keeping an inventory of colors I might want to use. Doesn’t make a whiff of difference to my finances.
By the way, a lot of filament you buy has been sitting on a shelf for 6-12 months and the desiccant and filament are already saturated when you get them.
@Ryan_Carlyle What a wonderful summary! It deserves a post of its own, so it can be found more easily, and read without dealing with adolescent rants… 
a guy named Deaths’ Klown giving unsolicited financial advice on a 3D printing forum
@mcdanlj agreed no time for trolls. Removed some of attention seeking post. Tried to only remove the rubbish and leave the ones with some actual content but he clearly has issues so blocked removed and reported so that pulled all his posts.
My storage box keeps it at about 10-15% with a bag of gel in it. Just made this holder for a hygrometer the other day to go on the box… missing/deleted image from Google+
@Ryan_Carlyle Houston is terrible for storage. Besides 3d printing, we manufacture carbon fiber parts, and everyone in the industry is concentrated out in Arizona and New Mexico, we fight moisture they don’t even have to deal with