New to 3D printing and have a question about humidity and drying filaments.
I have the Sunlu S4 dryer, which can accommodate up to 4 spools. I have read that TPU filament needs to be close to 10% humidity. The S4 onlyh goes down to around 25% RH, and yet it is rated as being suitable for various filament types, including TPU. I am confused. The onscreen display on the S4 onlyo allows one to set the RH to 30% minimum. How do you then achiev less than 25% humidity for the spools? This is very confusing to me.
Also, what temperature does the TPU filament need to be dried at, and for how long? How do we figure out when enough is enough and then how does one get down to around 10-15% humidity for the TPU?
I am sure I have some blind spots on this topic, so any help is greatly appreciated.
I have a S4. I think your confusion is from the above “fact” you picked up someplace, but that isn’t how you dry filament. You can either follow the recommended time/temperature chart for the filament or do it by weight, you don’t do it by %RH of a meter in the same box. In the S4 that is just a maintenance mode to try and keep moisture out of the box, it isn’t how you measure drying or dryness.
Here’s a chart for you, I pulled it out of the S4 manual:
It is confusing since it shows what temp and time you need to have for each filament type. That much I understand. However, the whole point of achieving and maintaining a certain temperature for a length of time is simply a means to achieving a humidity level, which for TPU I understand to be less than 15%. Let’s assume this is true. Therefore, after the recommended length of time, can one safvely assume that the TPU filament would be at the recommended dryness level? If so, then is it hence a case of puttingthe spool in a vacuum sealed bag and all would be good?
Well, you are complicating things by saying “assume this is true” but it isn’t true.
The point of drying is to remove absolute moisture, not relative moisture. And if the point was to remove relative moisture (a “humidity level”), you don’t have the equipment (or math) to measure it. If this isn’t clear, the moisture you are removing is independent of temperature, you care about the mass of water in the filament total, not the relative capacity of the filament to hold moisture. Those are very different numbers.
Um, honestly, no. But it usually is. To find out for sure, you need to weight the filament before you start and keep drying it till it stops losing mass. In lieu of this, just try the recommended table and if it doesn’t work, try longer.
If you want to store it, yes, just put it in a vacuum bag (or other container) with some fresh desiccant. TPU is so fast at absorbing moisture I print it directly out of the dryer.
That is very incorrect misinformation. I say that for the OP’s benefit and not as a reply.
I exclusively dry to a humidity level in the filament dryer - 19-20% and so far that has been plenty to not see water effects in my prints.
Drying by weight is actually pretty misleading. You don’t know the starting water weight and you don’t know the final. You only know the difference and a small difference can be due to poor drying or already “dry” filament. One is good and the other is bad. Weight can’t tell you which is which.
The humidity in the drying chamber, on the other hand, is directly related to moisture content. The issue is it’s also at increased temperature and the water is actually in flux. It’s coming out of the filament as it’s getting removed by diffusion or by a fan or whatever. But humidity is related to moisture content and can be used as a guide to when filament is dry enough.
Yep, people like you don’t believe it but if you would just have a look see at the literature on desiccants (and filament is essentially a desiccant) you would see you are wrong about this.
You weigh your filament before and after drying - a full spool - and only see a 0.1g difference. Is your filament dry? Yes or no?
This is the method you said is the only way to know if your filament dried. Did it?
Understood. It makes sense to not weight a spool before and after, since there is no way to know whether the desired dryness level has been achieved or not. The weight difference could be 10 g or 100 g…who is to say what weight difference corresponds to what moisture level?
The relative humitidty inside the dryer box (S4 in my case) being 20% could mean the spool itself is at 20% or 19 or 15% or less or more. And this is what I am trying to understand - if one were to assume the data (50-55° celsius temperature for 6-7 hours will yield the desired dryness in TPU filament) as gospel, how do we know for sure that we have the correct moisture level? The S4 only goes down to 30% when in maintenance mode. How is one to use this dryer to achieve and maintain 10% moisture for TPU? There is obviously a connection between an object’s actual moisture %age and the relative humidity of the container it is in, but I am not sure how to know what it is.
Therefore, using Occam’s razor seems to be the best course of action here - I will run the dryer for the recommended amount of time at the temperature listed, and then store the TPU in a vac sealed bag. And then…hope for the best.
Thank you all for chiming in. Being a noob and a hobbyist, this is something that I very much look forward to learning and playing around with.
First, it gets confusing when people tell you that PLA for example doesn’t have water effects and you don’t need to worry about it. That can easily be true for them but not true for you. Or maybe it is. But those who don’t understand others can have different results also don’t understand why.
The big variable is ambient humidity. Think of how sweat doesn’t evaporate well on humid days, or clothes take longer to dry. Ambient humidity puts a floor on how well and how fast you can dry.
Keeping that in mind, if humidity can affect how fast filament dries (it does), just drying for some amount of time at some temperature can get you different results if your humidity fluctuates. But maybe you have consistent low humidity. If you do, it could be following the recipes is all you need.
I can’t give you advice on the settings for the S4. I have no experience with them.
I’ve been looking for humidity vs moisture content graphs for PLA to show it behaves like desiccants. This one is for fine diameter PLA used for surgical sutures and they were looking at variations due to crystallization levels but they show behavior similar to other desiccants. What’s important is for every humidity there is a moisture content. If you know the equilibrium humidity you know the moisture content. There’s more wrapped up in it but this is why humidity can be used as an indirect measure of filament moisture content. It’s obvious (or should be) that low humidity indicates low moisture content.
And yes, it is a bit of a misnomer to talk about the humidity of filament. What that actually means is if you put the filament in a sealed container, the filament will either give up or take up water until the humidity in the box is appropriate for the water content in the filament. That’s actually the basis for a simple test to get a handle on moisture content - just add a hygrometer and read the number after it stops changing.
You have to start somewhere if you’re seeing water issues. Everyone can do as they please. You just want to do it with accurate information.
That experiment is driven in the other direction. The chart you have above is water absorbed by exposure to this RH, not water contained in the filament when a hygrometer measures this reading in a bag. It’s also with an equilibrium of… 4 weeks.
The water content and equilibrium humidity are linked and the relationship is as given for those particular filaments. It’s a physical property of the material. It doesn’t matter which way you come at it. It’s how that stuff works and if you would take the time to read more about desiccant behavior you wouldn’t be arguing the point.
Curious how while ridiculing the measurement you are acknowledging that it works but just want to exaggerate the time period. I’ve actually done the experiment. With the hygrometer I use it takes about 10-12 hours for the number to stop changing at least on any practical time scale.
Is the value still changing? Probably. These are processes that are driven by the differences. The smaller the difference, the less driving force there is. But as long as you do the measurement the same each time, you could compare results after the first hour. You can still get a good/bad kind of reading which is really all we care about. What the actual water content is doesn’t matter. What matters is knowing the water content is below whatever threshold it needs to be to print properly. You are overcomplicating this and missing the point.
I’ve never said it doesn’t “work” in the sense that there is a unique sorption isotherm for each material. What I said is that your idea seems unlikely to be a useful technique that people can practically apply. Not only is the EMC going to vary with each material, the absorption and desorption curves of material as complex as PLA or TPU are likely to contain significant hysteresis. Filaments are not desiccants, their sorption properties are mediated by much more complex factors than simple van der Waals forces. Note also I said “unique isotherm”, and I emphasize isotherm. As I mentioned before, these measurements are likely to be strongly temperature dependent, a fact you continue to ignore.
I understand it is your pet idea, but I think you are misleading people, especially beginners who think you are giving them actionable advice. You aren’t. It’s a fringe idea and there is a reason people disagree with you.
So OP asked what RH he should dry his TPU to in his S4. Go ahead, answer him.
Really? It sure sounded like you were saying it didn’t work. Only now, this time, you are allowing that it’s true after putting you in a corner. And now I see you’ve edited your post to hide what you said. Too bad I quoted you, huh?
And now you say I’m misleading people? You’re the one who said humidity had nothing to do with moisture content. That is incorrect - it’s a physical property. You went on about not using the humidity meters that all filament dryers have. You said that all OP needed to do was weigh filament before and after drying to know water content and never answered what a 0.1g loss means. It’s because you can’t. Two scenarios can cause that and weight alone won’t tell you. When put in a corner you tried to claim the measurement took four days when you hopefully know better than that. Again, who is misinforming and who is misleading?
What I was doing was correcting your misinformation. There actually is a reason to include hygrometers like all filament dryers do. They tell you a lot if you know what they are measuring. That you don’t understand how to use them isn’t an indictment of the hygrometers or the dryer manufacturers.
As to your question about TPU, I have no idea. Unlike you, I won’t go make up some cockamamie answer and try to pass it off as fact. That you don’t understand what I’ve said about drying is on you, bub.
I don’t know what humidity to dry TPU to but I know there is a value that if dried to should stop water issues. What I was correcting was you with your hat tip to our previous discussions where you were also wrong. OP was asking how to know if filament was dry. You gave him pure bunkum for an answer and I corrected you, again.
Humidity and moisture content are related. Weight alone does not tell you how much moisture remains in a filament. Putting filament into a dryer at X degrees for Y hours does not guarantee filament is dry. Ambient humidity has a big influence on drying time and whether filament will dry at all. Just because you don’t understand these things doesn’t mean it isn’t all true.
At least you didn’t try to explain it with a collection of pans of water.
Need to be careful, though. If you know your dryer will dry filament properly, then if you see a big loss or a small one you can still know you dried successfully but that’s a big ask. You have to know drying is working to use weight. If you know drying is working, though, you don’t need the weights.
Big weight loss is indicative of good drying. The real test is if filament prints properly.
The best thing to do is just try drying and see how it prints but keep tabs on the conditions. Keep track of the weights too. You’ll know if you are doing enough if you get good prints or not and what correlates with that. Ultimately you want to know your drying gives you reliably dry filament. That’s the whole point. You want filament that you can count on to be dry.
@mugglesmuggle’s techniques won’t get you that unless you are in a dry climate where filament drying just works. If you are in a higher moisture environment, that’s where understanding these issues gets more important.
I own a Sunlu S4 and a Polymaker Polydryer. Both are filament manufactures. Both include RH meters. Neither, anyplace in the instructions, suggest determining filament dryness state or drying endpoints by using the meters. Both provide a table of drying times and temperatures.
I use dry boxes, boxes that hold up to eight opened spools of filament. Within the boxes I maintain a humidity, according to a hygrometer I have installed, from 15 to 20% by use of 50 gram Dry & Dry desiccant packets. There is a direct correlation between the weight of the packets and the humidity in the boxes. As the humidity nears 20% the weight of each packet will exceed 60 grams. By recharging the packets, which reduces their weight to 50 grams, and reinstalling them, several in each box, the humidity in the boxes will drop to 15% or below. Using the same method I also keep the inside of my AMS units at around 10-12%. I use PLA and PETG and have never had an issue with moisture in my filament.
I have a filament dryer, a double Creality space Pi, but have only used it once to dry filament, and that was just to see if it worked. I have created a couple of racks that hold desiccant packets and recharge them in the dryer. It takes considerably more time than the microwave, but then I don’t have to worry about the desiccant beads blowing up or melting down like they sometimes do in the microwave.
I see merit and value in all the responses. Yes, following the recipe’/guidelines will help, as has been suggested. However, now I also understand that just blindly following a set of data points is not necessarily a guarantee of the achievement of the desired results, but it is a good starting point for an ignoramus like me. I live in Eastern Montana, so our winters can be quite dry in the house (not as bad as the Midwest, though) and not as cold. I can easily maintain an RH of around 25-30% in a room…or increase it to 50-60% with humidifiers if needed.
The Litmus test will be the print quality. The TPU has been in the S4 since last night, first undergoing 6 hours of heating/drying treatment and now has been sitting in the dryer at around 25-30% RH.
I am going to go tot Home Depot and grab a transparent tote large enough to hold 4-6 filament spools in it with dessicant (thank you, 3dEd).
Thank you…I appreciate you all. EVERY. SINGLE. ONE. OF. YOU.
They might have anticipated/experienced few understanding the fine points of filament drying. Trust me - it’s exhausting when so many are so entrenched in the armchair science. It’s a complex topic that some are incapable of wrapping their head around. It could be they figured there’d be fewer customer support calls if they kept it simple for the people militant about just drying at a temperature for a time. That does work for some. I simply do not know their reasoning. I didn’t write their instructions.
Some manufacturers see the deficiencies in the common designs and try to fix things. Some are including desiccant in the dryer which apparently according to you isn’t needed. According to me it’s not the best place for it as the desiccant can hold more water at cooler temperatures. But they are getting more sophisticated in the designs and features.
Just look at all the people who dry according to the simple recipes - follow them to the letter - and still have moisture issues. That should make it clear there is a puzzle piece missing from the basic designs. If there wasn’t, drying at a temperature for some specified time would work for everyone.
At any rate, like with the guy with four pans of water, I’m tired of arguing with you. We’ve now walked you from denying humidity affects drying to grudgingly accepting and admitting it. Similarly, we have gotten you to acknowledge, again grudgingly, that there are curves that relate equilibrium humidity with moisture content. You are so close to enlightenment but refuse to go the last step. Whatever.
IMO, not worth bothering to store filament in a tub with desiccant, just get in the habit of drying your filament each time, before you use it. A plastic tub isn’t going to be at all “hermetic”. The desiccant will need constant attention because it’s going to absorb moisture from the filament and any moisture that leaks in through the not-very-tight lid seal.
The only filament you really have to worry about storing in a humid environment is PLA. It gets very brittle when it’s absorbed a lot of humidity. But I’ve got some filament that dates back to when I bought my first FDM printer in 2010, stored loose in a box in my basement (which does have a dehumidifier, but I keep it at 40% RH). It’s never gotten wet enough to fall apart. Still works just fine after 24 hours of baking in a dryer.
Also, you can’t over-dry filament. Put it in the dryer and leave the dryer on until you are ready to use the filament. Turn the dryer off, filament starts to cool down and absorb moisture again. You’ve defeated the purpose of drying.
Wintertime ambient humidity levels are low enough filament doesn’t typically need to be dried.
