What should the moisture content be for PLA and PETG?

Bambu Filament and Accesories Filament
1

My AMS2 Pro is showing about 20% even after drying overnight with 4 spools of PLA, is that where it should be? What about PETG?

2

20% is good enough I’d say. There are plenty of prints I’ve seen on Makerworld to add desiccant pods inside the AMS2. Putting some of those in will probably help get the humidity even lower. I’d say try printing a stringing test and see how it comes out. If you’re happy with it, then carry on and happy printing.

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3

I have printed the desiccant holders that go inside the spools. I have had occasional problems with prints and was wondering if it needed to be dried more.

4

This is an apples to oranges comparison. RH% has little bearing on actual filament moisture content. Yes, a spool kept in a dry vs moist environment will either shed or absorb moisture but the measurement of RH% only applies to the air not the actual filament.

Outside of expensive analytical equipment, there is only one way to determine moisture content and that is by weight. Even then, all you can do is weigh it, dry it and weigh it again. If it weighs less, then there was moisture present. If no weight is lost, there was little or no moisture in the filament to begin with.

So the next question you might ask, how long and at what temperature should I dry it. The answer to that is a mathematical one. There is a table on Bambu wiki. But these are only guidelines. The simple test is to start off with the recommended temps for the filament being dried. Weigh it over a few hours. After it stops losing weight, you know you’ve reached it’s driest point.

Interesting side note: 1g=1ml=1cc of water. So by comparison, if you remove 5g of moisture, that about a teaspoon of water that was in your spool. :wink:
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5

It’s about the same for both, you want less than .2%

(I’m going to revise that up to .2% from .1% as most people will get acceptable results at .2%)

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6

The humidity in the place where you store your filament is a decent proxy for the moisture content of the filament itself, as long as your filament has been stored there long enough to reach equilibrium. Here are some good general guidelines for PETG, depending upon the relative humidity in the location where you store your filament (PLA likely needs drying even less than PETG):

  • RH ≤ 20% You’ll keep PETG near its lowest achievable moisture content. Drying rarely needed if you maintain this level consistently.

  • RH 20–30% Moisture uptake stays very low (probably <0.15% by weight). Suitable for most prints; you can skip pre-drying unless you need maximum clarity or strength.

  • RH 30–50% Moisture content approaches ~0.2% (datasheet range). General-purpose prints will still look good, but highly detailed or optical parts may show stringing or hazing—consider drying if you see defects.

  • RH > 50% Uptake exceeds ~0.2%, and you risk bubbling, popping, and loss of tensile strength. Active drying or sealed storage with desiccant is recommended before printing.

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