I just finished drying a roll of asa last night, got it to 9%. Trying to dry a roll of PLA today. Its 8 hours in and still not under 27%… any ideas? It is humid outside, but it was last night as well. I know pla takes longer, but I would expect it to be lower by now. Its in an AMS HT. I dont usually dry my filament, I use it up pretty quick, but I’ve got some rolls that are going to sit a while, going to vacuum seal them with desiccant and put away.
Chances are that you are drying that ASA much hotter than the PLA.
Higher heat is faster drying.
It is, but I would just expect that if 12 hours was considered a full drying cycle for it to be at a lower percent by now.
Assuming you’re talking about humidity reading of the AMS (vs. an actual material probe like for wood moisture levels), that’s not a very useful metric. Keep in mind the reading is relative to the temperature of the air. 85°C air can hold a lot more moisture than 60°, therefore the relative reading will be lower for the same actual amount of water.
I think going by weight is a more definitive metric, even if it’s not a perfect “lab-level” solution. Weigh the spool before, during, and after a drying cycle. It should stop loosing weight at some point. Of course if it ends up absorbing moisture because it was already dryer than the environment… all bets are off! 
-Max
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The differences in humidity between PLA and ASA are likely due to the different drying temperatures when taking the measurement. You can use those numbers to know when dry enough but you need to be consistent in how you do it like not comparing filaments that dry at different temperatures at those different temperatures. But using an RH value for ASA as “dry” and a different number for PLA is valid.
The best way I’ve found to determine moisture levels in filament is to just put the spool in a sealing polyethylene cereal box with a hygrometer and read the humidity level at room temperature when it stops changing. The humidity reading is proportional to the filament moisture within filament families (like PLA, ASA, PETG, etc).
About using filament quick as a way to ensure dry filament is a misconception. The vacuum bags most filament is sealed in when new is semi-permeable to water. A sealed bag and desiccant pack is not a guarantee the filament is dry straight off the delivery truck. It may not even be dry when it’s put in the bag. I’ve used the test above on fresh/new filament and it’s not uncommon it tests out at too high of humidity.
For my conditions here and my X1C, PLA that tests out any higher than about 25% humidity at room temperature is too wet for me to get good prints. For PETG HF the go/no go is about 20% but in both cases, lower is better. If they test out below 10% (as low as my hygrometers read), there won’t be water effects in my prints. The 20% and 25% limits are the max I can use with minimal effects.
About drying, I did a deep dive a while back. My local humidity is around 40-45% or so and cannot store filament in the open without developing adhesion and print issues. I bought a Sunlu S2+ and followed multiple drying sessions with time lapse photos of the Sunlu display with a clock in the image and plotted them. I was also weighing the spool to follow the weight change. The Sunlu would dry until it hit a floor but not go any further. The humidity in the chamber and the mass would stop changing and it wasn’t good enough to eliminate water issues. Reduced but not eliminated.
What it took for my conditions was adding a low flow of dry air to the filament dryer. After everything plateaued out, when I added dry air the humidity in the Sunlu would drop again and continued dropping to around an 18% level at temperature which turns into below 10% at room temperature and no moisture artifacts for me at all. No calibrations aside from the initial unboxing setup, no special G-code. No teardowns and parts/belts replacements.
Last bit is weighing alone cannot tell you about drying techniques or filament moisture except hinting at where you might be water-wise. The reason is you don’t know the actual weight of water in the filament. All you know is how much was lost. If that number is “big” you have better confidence that a drying technique is removing water and possibly significant water, but you cannot nail down how much is left or if it will print well. There is no definitive there is X amount of water.
A humidity measurement also doesn’t tell you water content but it tells you a physical quantity that is proportional/related to the water content. That relationship is fixed by a moisture/humidity curve and we don’t even need to know what that curve looks like. You can treat humidity in a sealed plastic container with the filament and a hygrometer like water content in the filament and determine your own go/no go levels for your own printer and ambient conditions.
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Until is stops losing weight. That’s the key part. Of course some random absolute weight tells me nothing.
I’m not arguing the next points, mostly just curious… if it works for you then that’s what counts.
“Room temperature” is that in a climate controlled room or something? Or IOW, what’s the temperature range within which you consider comparing RH readings as valid?
How long do you keep it in the bag before being sure the RH stops changing?
And how is the hygrometer measuring RH if there’s a vacuum? (In an actual vacuum it requires special hygrometers.) And assuming there’s a physical passage for moisture from the filament to the hygrometer. EDIT: never mind, sorry, you didn’t say you vac. seal it.
Moisture capacity definitely varies less at lower temps, so differences within a set range like 20-22°C should indeed be minimal.
-Max
Until it stops losing weight tells you something but not as much as you seem to think. Weight tells you nothing about remaining water because you only know how much it lost. You don’t know where you started and don’t know where you ended. You only know the difference but where you end is what’s critical. Lose a lot of weight and your drying technique is probably pretty good but that’s the point - you don’t know if a spool was particularly wet or the dry went really well.
The weight method has been promoted here a lot but it is flawed because nothing pins it down. The only ones who can use only weight to know if their filament is dry are those who have good drying techniques that always produce dry enough filament when the weight stops changing.
But for those in humid environments, or that have lesser dryers, the weight can stop changing prematurely. I saw it. I documented it. Weight change does not guarantee dry filament except for those who have good drying technique. That’s the important point. Those with poor dryers or poor techniques will also see a plateau but it will be at higher moisture content. Their weight differences will generally be smaller but if the weight stopped changing, they still may not have dry filament even though everyone says when the weight stops changing they are done. They may not be.
Your point of view of “all bets are off” in the weighing to zero change is a good one. Without something to pin down how much water is in the filament, all bets are off and it reveals the flaw in weighing to zero change. Measure humidity and you have a real life honest to gosh data point that actually says something about filament moisture. Not a water quantity but a value tied directly to water quantity that can be used just as well as water quantity.
It’s like a gas gauge in your car. It says 1/2 full. Unless you know the relationship between remaining fuel and gauge reading, you don’t know how many liters or gallons are left in the tank but you don’t need to if you know at 1/2 full you can drive x miles or make it to some destination. Basically the same thing.
Room temperature is just a convenient temperature to use. Different filaments are dried at different temperatures and there is a fair dependence of RH% on temperature. Room temperature is usually taken as 25C but nothing especially rigorous about that. But in most rooms, temperature won’t be far from 25C. Generally not as far from 25C as one filament type is from another in drying temperature.
I use both room temperature measurements and at drying temperature measurements. You can. It’s just you have to keep in mind they aren’t directly comparable. My room doesn’t change temperature more than a few degrees when I’m using it, though - and that is close enough in my experience. Your graph shows how 25C isn’t on a steep part of the curve. It doesn’t make much difference.
As to time “in the bag”, I don’t use bags. I use thick wall polyethylene cereal storage boxes because water diffusion rates are extremely low. You can use bags but you need to be aware the water diffusion rate is much higher. If I take a gallon ziplock bag with a hygrometer in it and fill it with dry air, in about a day (at most two) it leaks in enough water the humidity inside is almost as high as outside. It’s why I can’t use bags for storage.
The hygrometer reading will change “fast” at first but slow as it gets closer to the actual humidity value. I went an hour or two max when checking it out. Much longer and it will be reflecting water infiltration. Too short and it won’t be as accurate as it could be.
As noted, I’m doing none of this in vacuum. All is at ambient pressure.
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Thanks for all the replies. I live in FL and my H2S lives in the garage, so humidity is expected. Aside from 1 really wet roll of PLA, I haven’t had much issue in prints other that it failing to do any significant overhangs without supports and some stringing. I’m drying and sealing some of my roll that I dont have a plan for at the moment an trying to save them. I’m using vacuum sealed bags with a container of desiccant and a hygrometer. We will see how well that works.
Neither option measures effectiveness of a drying run w/out knowing the absolute lowest possible range (weight or released moisture afterwards in a container). Of course combining the techniques also helps, but nothing is absolute.
In case of humidity level check I could see it also being useful to perform the test before drying as well. Otherwise how to know anything changed?
Sorry, I misread the “bag” part (again) somehow… you didn’t mention a bag originally, only a container.
From my experience I’m not sure 1-2 hours is really enough to stabilize RH readings, but that’s something fairly easy to establish with a given hygrometer and container.
IMHO it’s simpler to put the spool on a scale to check if it has stopped changing, w/out stopping the dry cycle, vs. sealing in a container for a few hours first. But I’m not promoting anything. YMMV.
Cheers,
-Max
I’m also thinking this roll of PLA is as dry as its going to get, coming up on 36 hours in the dryer at 65C. I know the outside humidity also plays a role in how dry it will get, and being FL, I wont hit ideal numbers.
That’s not actually true though. Humidity measurement in a sealed container is directly related to the filament moisture content by a curve that can be determined empirically that relates equilibrium humidity with moisture content. There’s tons of literature about those curves for all sorts of desiccants which are used in many industries to hold humidity static at some value, high, low, or mid-range for all sorts of reasons. Combining with weight has uses too. And for those that have good drying setups that using weight change to know when it’s done is sufficient as long as the drying setup eventually would get filament dry enough anyway.
And granted, testing humidity is a slow process depending on a number of factors. The meters start responding quick to big changes but just take a while to reach the steady state value. If the swing and magnitude are screaming a spool is wet or dry, then you don’t need to test for long for go/no go things. If you have a specific value that you have experience with causing issues and you’re close to that line, then you may want to let it settle more. Seems settling time gets longer the closer you are to 0% RH.
But for sorting out drying setups, humidity will tell you things weight can’t.
It also provides insights into just how wet filament can be coming out of that sealed factory bag with a pack of desiccant in there. There’s many new to all this that assume it’s dry when it may not be. It’s an easy test to do and can explain a lot when you see it with your own eyes.
That is one thing weighing can tell you - if the weight has stopped changing, you won’t remove more water by continuing the drying process.
Ambient humidity has a significant effect on the effectiveness of most drying processes/setups. Most have experienced a sweaty shirt on a humid day. Sticky and slow to fully dry. On a dry day, though, the shirt dries fairly quick and more than on a humid day.
Temperature in the dryer lowering the RH definitely helps but can only go so far especially at low drying temperatures on some filaments.
Unfortunately, high ambient humidity slows and limits the dry. It’s why manufacturers resort to other strategies like desiccants or permeable membranes, and other approaches in the higher end dryers. Those in high humidity environments have to deal somehow with the water with dehumidifiers and other approaches until they get the print results they want.
I dry everything for 8 hours, but use appropriate temps. For PLA I use 55c, and petg is 65c.
My area is quite humid, so in the AMS2 or Polydryer I dry for 24hrs. In the AMS-HT 12 seems to be sufficient.