A possible way to estimate water content in filaments

Bambu Lab P1 Series General Discussions
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Just putting this out there but while working with my poly cereal boxes, I put a spool of fresh PETG HF from its poly bag into a cereal box without a desiccant pack and was surprised to see the humidity in the poly box start climbing up.

Just checked this morning and ambient humidity in the room is 39%, the spool of PETG HF in a poly container is showing 42%, and a spool of ASA that I had dried for a few hours yesterday is showing 25% RH in a poly cereal box. Again, no desiccant to scavenge out water.

I think poly boxes without desiccant might be a way to get a handle on water content in filament by putting a spool in a poly container with a hygrometer, closing it up, and let it equilibrate to a stable humidity reading. The humidity should be a function of water content in the filament and may get skewed with cardboard hubs and spools but still should give an idea of how wet the filament is.

I doubt you can directly compare moisture contents from one filament type to another but within a family like PLA, you can probably say if one spool is wetter than another and people may be able to find humidity levels that predict if there will be printing issues or not.

We don’t have a way to determine actual water content in a filament but this might be a way to indirectly measure water content without having to dry to get a weight change, etc. Everything else has been a change - how much water was lost and so on but nothing to actually get a handle on water content. This might give a number related to actual water content.

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I’m sure they’ll find a way to do it reliably, the day before they release hydrophobic filament. I try not to overthink it and weigh/dry/weigh for a 6hr cycle initially then keep the coil in a reasonably stable state till its used up. Sometimes it gets a few topup treatments along the way if defects show up.

I think the cost of testing and the intervention is the prohibitive, particularly when you can only test the outer few layers if the coil is wound reasonably well. Same goes for drying for most of us I think getting the extremes would be a bit too destructive.

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I don’t see the destructive aspect. I think actually getting a handle on water content in filament can prevent 24 hour and longer cooks which reportedly can damage filament through “overdrying” (I’m not sure there is such a thing. It’s more likely thermal degredation.).

Anyway, playing around more with this, I dried a spool of brown PETG HF yesterday to 24% RH in the drying chamber (experimenting with how much drying is needed and hit 24% in about 5 hours with dry air purge. This morning I put the orange PETG HF in the dryer and put the spool of brown PETG HF in the poly box the orange came out of and in about a half hour the humidity fell from 42% to now showing 10% - the lowest the hygrometer will indicate.

That’s at room temperature while the drying was a 55C when I pulled it at 24% RH. RH has a big temperature dependence.

So fresh from the bag orange PETG HF stabilized at 42% RH overnight while dried PETG HF is now showing below 10% RH. Looks like it’s doing a good job of saying which spool was dried and which wasn’t.

As to cost, these poly boxes are just a few dollars each at Amazon and the hygrometers are about a dollar. That’s how much this test costs plus some time for things to equilibrate.

It’s not overthinking it, either. While you may not have issues with moisture, lots of other people do. This is an indirect measure of moisture content in filament. That’s a question a lot of people have. Many are unsure if their drying technique is actually drying. This can tell them for even less money than buying a good scale. It can also be used as a diagnostic, albeit slow, if a particular filament isn’t printing properly. Just check its humidity in a closed impermeable box.

What is missing is some kind of guidance on what humidity levels with each filament type start having issues with printing defects. That can come as people get experience.

But the test itself is trivially easy, many already have the bits to do this, and so far it’s working really well. That I can put dried spools in and it pegs the hygrometer low while undried spools are testing out with water content seems to show it’s working. That I can put a dried spool in and it pegs the hygrometer low is just more validation my drying technique is also working.

I’m really curious what others will find but this is looking good. It’s not destructive. It’s trivially cheap. You don’t have to believe it or do it. If your drying is working for you, great, but if you check the threads here, you’re an outlier.

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A possible way to estimate water content in filaments

Erm, suck hard, really hard?

I had to say it, before some else did.

Now, smart people you may continue, the moron has left the building.

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There are tools specifically designed to test the water content of solids. Generally classified as “Moisture Meters”. Get one of those, it ought to work on plastic same as it works on anything else that can absorb moisture. Like dirt and wood and sheetrock.

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I don’t need a moisture meter. The way I dry my filament works great.

Out of curiosity I looked up models that would be appropriate for plastics and they are thousands of dollars. Moisture meters you stab into wood are not appropriate for plastics is my understanding. If you know better, please enlighten. Maybe you know of or have a cheaper one that works.

The purpose of the original post was there have been lots of issues with filament drying and things like scales don’t tell you much if there isn’t much weight change during drying and prints still have issues.

Many have the poly boxes and hygrometers and I noticed the relationship between wet/dry and humidity in a poly box with no desiccant. It’s a trivially easy test that many already have what they need to try.

But I luckily I don’t need to even use this technique. As I said, my filament is “dry” and prints great. I just thought it could help others. If your moisture meter is a good deal that would benefit the community, you should start your own thread with all the details about how well it works for you, and how it has helped with filament drying, if it has helped with filament drying.

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I just throw the spool in the dryer while I’m finishing up my CAD work, a day or so in advance of when I’ll be printing. No worrying about how to store the filament to keep it dry. No worrying about how dry it may or may not be. All that matters is the storage is relatively dust-free.

So I don’t need a moisture meter, either. The way I dry my filament works great.

:slight_smile:

AI says this about that, though:

Yes, you can use a less expensive moisture meter for 3D printing plastic filament, but it may not be as accurate as specialized meters. Some users have found success using general moisture meters designed for wood or concrete, which can be quite affordable (around $20-$50). However, these meters might not provide precise measurements for filament moisture content.

Another option is to use a filament dryer, which can help reduce moisture in your filament. Devices like the Matterhackers PrintDry PRO are available for under $250 and can hold multiple spools of filament at once. While this doesn’t measure moisture content directly, it helps ensure your filament is dry and ready for printing.

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So, you don’t have drying issues, don’t have experience with measuring moisture or know why cheap meters for wood and drywall don’t work well with plastic, and even your AI source tells you that regular meters are inaccurate with plastics when asked again?

Meanwhile, this thread is about dunking a spool in a poly box, waiting, and reading a number. No comments about that except go buy a tool that doesn’t work for this application? Ever helpful.

How is it better to advise people to spend hundreds to thousands on a meter just because you heard of it somewhere and take what AI says at face value even if it’s wrong?

It’s great you don’t have filament moisture issues. If you read through many posts here you would see quite a few do have those problems. As strange as it may seem, I wasn’t talking to you when I started this thread you ■■■■ on. :grin::grin::grin: (I can also include smileys) It was an attempt to help the people with filament moisture issues while you jump in and send them on a wild goose chase.

Learn to check your AI answers before you spread them like gospel. AI is trained on very flawed data sets. Just like the pictures it draws with too many fingers or arms, in this case it seems to have told you to use the wrong tool. Only when you asked it again did it say a regular moisture meter might give inaccurate data.

Here’s a thought - go read some actual plastics industry literature on how they test and control moisture because they sure do. They have the same water issues we do when hot plastic gets injected into molds and have decades of experience. Had you done that instead of polluting this thread with AI bull because you wanted to make some point, you would have seen right off that they say you can’t use regular moisture meters for plastics. Part of the reason is the conductivity ranges are very different. Ask your AI what that means.

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And since you are touting the benefits of AI and how to dry filament, can you tell us why that Matterhackers dryer is not ideal? Or any of the common filament dryers? Do you even understand what this thread is about?

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@MZip
Thanx for the great articles about drying. Just stumbled on this topic and decided to try this.
Background: I live on the coast in high humidity area. Curenty outside is 9 °C and around 90%+ RH, and it’s been like 60-80%+ for a couple of weeks :slight_smile:
So storing and drying the filaments has been a challenge.
I have one roll of PETG that a couple of months ago was not printing well oob. It has later been dried and stored in vacuum sealed bag with no dessicant and was not used afterwards. It was in the my esun dryer with fan for 8h, lost 2g and again the next day for 12h, this time without any weight loss. The bag held fine all this time.
Yesterday i put one of my BLE connected higrometers in that bag and sealed it again. Inside the storage room I got 50-60%+ RH.
On the attached graph, yesterday around 8 (AM), reading stabilized around 54%. Didn’t vacuum it at first. The small notch at 20h (8PM) is when I decided to pull some air out with vacuum pump. The bag was not opened and vacuum holds fine. No significant changes in the past 24h.
In that room is currently 66% RH and while I’m writing this it stared raining outside so RH went to almost 100.
What do you think about that almost constant 54%?
The higrometer i believe is precise, the values don’t deviate too much with other ones i have at home.

Screenshot_2025-02-11_08-51-55
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I’m not sure I’m understanding? The hygrometer was inside the bag that you later vacuumed down.

Something @NeverDie warned me about some months back is we were looking at storage and moisture and he said if you flush a Ziplock bag with dry air and put a hygrometer in there but no desiccant, it moves to ambient room humidity in a day or two. The plastic they use to make the bag is somewhat permeable.

It’s not quite as bad with poly cereal boxes but they leak down too and water crosses into those even though they are sealed in weeks to months. I ran out of fresh silica gel as I was drying all my filament so had some cereal boxes with just dried filament in them. I’ve been going back to those boxen without silica gel to scavenge water and their humidities are high 20s to low 30s RH% after 3-5 months where they had pulled down below the 10% mark originally.

If you are wondering about humidity inside of plastic containers, some/many allow water to cross their walls. Silica gel may be necessary in containers to scavenge water and keep humidity from rising inside filament storage bags/boxes. It seems to be for me. All my filament with silica gel in the boxen still reports at 10%. The few without silica gel creep up in humidity.

As for storage at 54% it’s hard for me to say. Probably depends on the type of filament if you can expect water issues but I would guess so. That’s around what my ambient humidity was when I had water issues show up. High 40s to low 50s give or take probably.

My opinion now is with “moderate” humidity levels, at least with the poly cereal boxes, some silica gel is needed in each box to grab water in the box. Without desiccant in them, humidities can rise and filament can reabsorb water.

Is that what you are getting at?

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Sorry if I wasn’t clear. English is not my native language :slight_smile:
I was looking for a way to reassess the filament’s humidity after several months in a vacuum-sealed bag.
I suspected that after a few months, the filament might have somehow reabsorbed moisture inside the bag. Either that, or it was never properly dried due to higher ambient humidity. I have some PETG stored in vacuum bags with silica. I’ll have to check those.
I’ve had some failures with those cheap vacuum bags where the seal failed, causing the bag to soften and inflate. I would never have thought the bags could be permeable :slight_smile:
Thanks, I’ll try using the cereal box. It’s made of hard plastic and has a good seal.

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Ah. I’d still say hygrometer in the bag/box with the filament to get an idea of filament moisture. If you’re asking if 54% is too high for that measurement my guess would be likely. It may take a while for filament to act up at that storage humidity. Not much experience with how much is too much, though. At lower humidity water effects will take longer to appear so time is a variable too.

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I am contemplating this as well, and am working on a proof of concept to detect moisture via weight, as @MZip mentioned above.

Here’s my plan for the process:

  1. Record the initial weight when the spool arrives
  2. Dry the filament, and weigh immediately after
  3. (optional) measure RH without desiccant and record that with the weight
  4. Before use weigh the filament again and calculate RH based on changes in weight
  5. (optional) compare to RH without desiccant
  6. complete print, and start over from step 1

The key here is measuring the difference in weight from when the spool was put into storage and when it is being taken out of storage.

This is all very cumbersome to do manually, so I am working on developing a software solution to help with this, and looking for ways to streamline the process once that is in place.

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That’s a difficult calculation. The RH value in the test is related to filament moisture but we don’t know the relationship between RH% and moisture content in the filament. All the RH% really is is a go/no-go level to use to decide if you need to dry your filament. And until people get experience with it, it’s going to be very fuzzy.

And it should be noted that it appears you can calibrate out some bad moisture behavior. So depending on how much fiddling people are willing to do, it could be some can call it at higher RH% levels just because they have calibrated out some level of moisture. Tolerable moisture levels may depend on all sorts of things - ambient temperature, doors open or closed, characteristics of the filament and characteristics of the model and print conditions.

And to be accurate, we all have some level of moisture in our filament. It’s just if it shows problems when printing.

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Totally agree, thinking a good estimate can be derived through trend observation by tracking when prints fail, as well as measuring correlation between weight gain and measured RH with a hygrometer.

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Could you please share a link to the ones you like?

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I recently started this wonderful and frustrating hobby, my first 3D print was on 2/28/25, but I have been looking into 3D printing for months, mostly researching if it’s feasible for me and my wants & needs. Very early into reading about BBL, I came to terms with time spent dealing with RH in spools for this hobby, so I made myself this spreadsheet to track all my spools, my reusable spools have been numbered, I took all their weight when I removed them from their incoming packaging, then after an 8 hour drying cycle inside a Polymaker Polydryer, and either left them in the Polyboxes, switched them to a large dry container with an abundant amount of desiccant, or left them inside the AMS (also with an abundant amount of desiccant).

I’ve not only been measuring the weight pre and post drying, but also my filament usage in grams for each spool, on a per print basis. Once I’m done with the spool, I measure the weight as well, and update the spreadsheet.

I do note a weight difference from 8 hours drying, so I know these spools are losing some humidity, but I’m starting to think this method might not be accurate enough for anything other than tracking an inaccurate quantity of filament left on a spool, or if I have dried them or not.

I also started to weigh the spools inside the Polydryer box, in conjunction to the spool itself, I’m trying to make it faster for me to determine RH loss, but I think the desiccant inside the Polydryer box might be making the RH change in the spool erroneous, simply by measuring the weight alone.

This is most likely a flawed way to attempt this, but it’s how I started. I’m sure there’s something better than this out there, but hopefully it’ll give someone an idea to improve upon this.

Note: Unfortunately my scale doesn’t measure milligrams, and is essentially another added inaccuracy to this.

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If you are measuring the weight of the spool inside of the box, I assume that includes the desiccant as well. If so, then measuring the weight won’t tell you anything, because any moisture that is extracted from the filament just ends up in the desiccant, resulting in no weight change. I think you would need to remove the spool from the box to weigh it to get actually see if the amount of water in has changed.

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I agree. I am doing both though, I’m measuring the spool by itself and then the spool inside the box. I have noticed that even inside the box there is a change in weight, but the difference in weight is indeed different from the two. For instance, my ASA spool arrived weighing 1266g (2013g inside the box), after 8 hours of drying the spool itself was 1263g (2011g inside the box), so there’s about 1g of difference in weight between it being inside the box and the spool by itself.

It’s quite fair to say that this whole exercise was moot and inaccurate, I’m also new to testing stuff like this, but it has helped me get more familiar with things.

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