I have not experienced adverse consequences from “overdrying” any of HS-PLA, HS-PETG, or PPS-CF, all of which I typically dry for 2 or 3 days, but sometimes much longer just out of neglect. I can even heat the HS-PLA and HS-PETG at 65C seemingly forever without adverse effect, even though this temperature is much higher than typically recommended for PLA or PETG.
That said, I did see a youtube video which says that Nylon, in particular, can be overdried, and that it becomes brittle when overdried. At the same time, if left to rehydrate from atmospheric moisture, it was shown to become “restored” and bendable/flexible again. If I could remember which youtube it was, I would post the link. I don’t have all that much experience with nylon, so I can’t verify the claim myself. Unfortunately, I don’t remember which blend of nylon it was, either, which might well be a factor too. Suffice it to say that it is an existence proof that at least one type of filament can apparently be overdried to the point of becoming too brittle to feed through a PTFE tube without breaking while in its overdried state.
On a different topic, but worthy of note because it’s something I only recently learned: HS-PLA is reported by some to be far more hydrophilic than ordinary pure plain PLA, and this does match my own experience with it as well. I haven’t seen this talked about on the forum, and I don’t think Bambulab even makes such a PLA (unless their regular PLA is, in fact, HS-PLA, who knows?). For cost reasons I haven’t been using Bambulab PLA, so I can comment on that either.
Naturally, I would encourage anyone and everyone to post their experience as well on the topic of overdrying so that we can pool our knowledge/experience and learn together.
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Nylon, TPU, PVA, PC, and PETG are all hydroscopic, and they rely on small amounts of moisture for flexibility so yes, excessive drying can make them stiff or brittle, except PVA which crumbles if it’s too dry. PETG is only minimally effected, it looses flexibility but too dry can actually enhance stringing same as if it’s too wet.
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Ah! I may have ran into this when working with some TPU 72D. I left it in the drier for a couple days to ensure it was dry (not originally planned, just lost track of time) and it printed like it was wet (stringy). So maybe that is what I experienced?
I will have to try that roll again without drying it (it has been just sitting out for a week now).
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@RocketSled
So how exactly can we arrive at the right goldilocks level of drying for PETG? Not too wet and yet not too dry? What is the best/optimal procedure/algorithm for doing a proper job of drying PETG? Or, if unknown, what are people here doing that at least seems to work best for them?
If overdried, does PETG rehabilitate to fully viable again by exposure to atmospheric moisture the way the Nylon in that youtube I referenced in my first post seemingly does? Or is it basically ruined if overdried and nothing can be done about it after the fact?
You can’t. But I wouldn’t worry about it unless you’re vacuum drying. Most dryers just heat the air. That drives moisture out of the filament through diffusion. But the humidity level of the ambient air still limits how much moisture can be removed from the plastic. No way you can get it to zero (or even all that close to zero).
I typically throw my PA and PETG in my Sunlu driers at 65ºC for 24 hours. I haven’t had any problems with this methodology.
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I’ve gotten some engineering filaments that had a warning “do not dry unless signs of moisture” but I can’t remember which ones.