Once PLA gets brittle like that, it's usually because the polymer chains have broken down (hydrolysis) which no amout of drying can fix - the chemical damage is permanent.
this post was submitted on 27 Jul 2025
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Assume you tried unraveling to deeper layers? If it's brittle beyond the surface layer in the spool I think it's toast. Would be interested to hear the trick if I'm wrong.
There's probably only 150g or less on the spool so I did not unravel it. After the 12 hour bake I gave the very end a bend and it snapped like a twig. It's running at 55c and 15% humidity right now so here's hoping. If it's screwed it's not the worst thing ever, but I have nearly 1kg left of old ABS as well and I would be sad if I couldn't save it.
A trick is to weigh the filament before you start drying it and then weigh it again every few hours to see if it's stopped getting lighter. If it's been hours since it lost a single gram, then it's probably close enough to as dry as it's going to get, and if it still doesn't behave, then there must be a second problem.
I've just finished a roll of PLA that was laying around for 7 years or something like that. It was fine except first few layers on the spool and a bit dusty. On the other hand another spool from the same brand that wasn't even opened became weird and gooey mush.
The issue is not so much humidity as it's micro cracks. You can try annealing the PLA in an oven. Try it repeatedly, increasing the temperature by 5°C each time. Should be fine at the latest at 70-75°C, but this might also change the dimensions of the filament, making it unusable.
But filament is so cheap that it's likely not worth the time and the electricity to try to fix small left-overs.
PLA has a shelf life, it does degrade a little especially if in a room that had sunlight. Over 3-4 years old it may not ever be usable.
You may need a very long dry time (multiple days) due to the spool likely being wet completely throughout.
Yeah that makes sense. Do you think the ABS would be more salvageable?
The ABS is more likely to be usable after drying.
Awesome thanks.
This is helpful. I'm just about to start a print with 2 year old filament.