The advice to use a food dehydrator with adjustable temperature settings is a great one. For a general guideline, you can follow these temperatures and times:

PLA: 45-50°C (113-122°F) for 4-6 hours

PETG: 60-65°C (140-149°F) for 6-8 hours

Nylon: 70-80°C (158-176°F) for 8-12 hours It's always a good idea to experiment with what works best for your specific setup.

I've had some PLA that became so brittle and crumbly that I couldn't use it, and over-drying might have been part of its path to that state, but PETG in particular starts out tough and flexible enough that it can take a _lot_ of drying prior to printing.

What would be a concern is if the heat were sufficient to dissociate the polymer or otherwise change its physical properties in a way that would persist across melting, but IME that's not what we're talking about here.

The trickier materials are the ones like Nylon that require a small amount of moisture for flexibility, but that print very poorly with any more than that. A while back I experimented with molecular sieve desiccants and managed to over-dry some PC-CF and PA-CF without even heating them. Molecular sieve desiccants are famous for being able to suck all of the moisture out of even other desiccants given enough time. The RH in my storage box got down to ~2% (measured using a very accurate hygrometer) and weird things started happening. Also, Prusa filament spools with cardboard cores tend to fall apart if you to such low humidities.

 

Posted by: @bunny-science

My temperatures and processing times

TPU 129F (54C) x 10 to 24 hours -- low temperature means extended drying time. Still stringy even when dry.

Hi Bunny-Science,

in very short, your TPU is "still stringy even when dry" for a specific reason: it's not dry.

54C is way too low of a temperature to dry it.

TPU absorbs moisture almost as fast as Nylon and is almost as vicious.
Saturated TPU will NOT be dry even after 24 hours at 70C.

Lightly moist TPU might benefit from staying at 54C for 24 hours IF THE AIR IS VERY DRY IN YOUR LOCATION.
Most places, though, are not bone dry as the air from desert locations and if your relative humidity hovers around 55% at 20C you WON'T BE ABLE TO DRY TPU EFFECTIVELY EVEN AT 70C in your oven.

The only effective way I found, is to place TPU in the aerated oven at 100C for at least three hours. Of course, you need to reinforce the spool with wood plates. The filament won't warp at 100C, but the spool will certainly warp otherwise.
I now use cardboard spools, these hold 100C indefinitely without warping.

Posted by: @snuffleupagus

@dimprov

 

If Swiss_Cheese could still be here, he would be Proud of you.

What happened to him?

If Swiss_Cheese could still be here, he would be Proud of you.

https://www.youtube.com/watch?v=eqQRN9TUw08

Thank you so much for doing the work. 

I have a question-do you cool the filament before bagging it, or put it into the bags right out of the oven?

@technogeeky

Well I'm glad someone was able to confirm that the unit I bought had solid temp control. haha. 
Where in the Dehydrator did you measure the temperature at? I'm wondering how much of a delta there is from the bottom to the top. 

I measured it down where I expect the bulk of filament in the first roll would sit. Having said that, it seems pretty consistent in all positions except the ouside edges where it is a bit warmer.

I actually finished my testing yesterday with a few 1 hour setpoint tests. As I mentioned before, the unit has about a 5F offset (which grows to about 6F at the highest settings).

I wanted to confirm that temperature regulation was good at various temperatures (not just that it is powerful enough to hit 80 C) - or more specifically that temperature regulation is consistent across the whole range (e.g. it's linear but with an offset). This is the case.

1. I set it to the lowest temperature supported, 95 F or 35 C. This isn't perhaps useful for filament drying, but if it doesn't have any flaws at the low end it could build confidence.

Very good regulation, it stays about 5 F too high.

Then I transitioned to the temperature we'd probably use for PLA, but in this case I went ahead and compensated for the 5 degree offset. So I set it to 144 F expecting to hit 149 F (or 65 C). You can see it doesn't overshoot:

And finally we can see a full hour at this temperature (again, set to 144 F expecting to regulate at 149 F (65 C)):

And here we see, again, good temperature regulation. There is a bit of upward drift - by this point it looks like the offset might be a full 6 F (which matches the offset at max temp).

I would trust this unit (I misspelled it CORSI, it's COSORI apparently) across the whole range as long as you measure the offset of your unit first. If there's a way to trim it out, that would be nice but since it's linear it's not really critical to me.

edit: Man, the image settings on this forum are really bizzare. It looks like it hard resizes the maximum dimension to be 500px and ignores constraints.