I have a question about best way to store filament. I have maybe 10 reels of filament that I have not needed to use for 6+ months. A couple of the bags have lost their vacuum but the other eight or so still have a goodish vacuum. The thing is that all of these reels show 43-45% humidity.
I typically dry a filament and desiccant, then put them in a sealable bag along with a digital readout temp+humidity. I use a 50gram bag.
of reusable desiccant. In the photo the lower bag was done this morning it sits at 16%, the upper bag was done some 6 months ago and despite retaining a good vacuum is now indicating 45%.
So my question is if a small amount of vacuum has been lost, but still there isnt much air in the bag, why has the moisture content risen to the ambient moisture in the room?
In a way this defeats the storage method, because now I have to dry the filament before using. So are these bags resistant to loosing vacuum, but permeable to moisture? Beats me.
I dont have much storage space so dont have room for plastic containers. Thanks!
It does appear those bags are permeable to moisture. I would try a different brand bag and see if that helps. Alternatively, use a large plastic storage box to hold your reels.
In your reasoning, you’re forgetting that the filament itself continues to release moisture. Even if you dry it beforehand, you rarely reach the innermost layers of the spool. In practice, you probably wouldn’t ever notice it, but after such a long time in storage, it definitely stands out.
Vacuum only removes any water that might be in the air, not the water or moisture that’s already in the filament. That’s why your measurement method is too imprecise.
Plastic bags, especially when vacuum-sealed, also absorb moisture from the air - not through the sealed opening, but through the plastic itself, even if only a very small amount. But retailers who ship their goods on long sea journeys can tell you a thing or two about that.
Plastic is never completely moisture tight. Even “dense” plastics such as PE, PP, or PA allow water vapor to pass through. This means that water molecules can slowly diffuse through the material.
You might also want to check out this thread on the topic:
By the way, the “best method” - which you asked about - is to not let the storage / room get that moist in the first place: Find another place or use a dehumidifier. It’s always a 50/50 situation: Control the humidity in the room AND store the filament in bags or boxes.
You didn’t mention your environments normal humidity but I’m guessing it’s a swamp and in summer as the main problem, but others have good thoughts re: the waters already in the roll to begin with.
Seems like those bags aren’t too great. You can combine two not great solutions to get a decent one, usually. Stick all those, in their bags, in a tote that has a gasket. Those arent prefect either but the two together, with a little fresh dessicant of any kind, should really slow down environmental moisture. The tote creates still air around those bags so even if they’re mildly permeable there’s no ambient air sloshing around them (greatly reduced convection)
Thats the thing. A dehumidifier costs as much as a decent filament dryer.
I keep my office around 30 percent humidity. Not perfect for filament, but it considerably slows them down in soaking up water. (Helps if your central air is doing half the work). Side thought: I like this method, but some people are more sensitive to low humidity environments.
For more picky filament, 5 gallon home depot buckets and some desicant is the way to go. They seal much better than a lot of the totes and can hold 6 or 7 spools.
Those bags are surprisingly permeable for water vapor. If you want a really vapor resistant solution, you need mylar bags. They have a metal coating that completely blocks vapor. Or you regularly exchange the desiccant as soon as humidity starts to raise inside. I also think that having a vacuum inside actually makes it worse, because that pulls the moisture in. I just pull enough air out of the bags so that it doesn’t take up extra space.
H20 is a smaller molecule than N2 or O2 and will leak in faster than air. The plastic bags are semi-permeable to water. And Sharky is absolutely correct that even polyethylene cereal boxes still leak water. It’s just the walls are so thick it’s very slow.
So double or triple bagging will definitely help. Each layer is not only a barrier but sets up a new region of low humidity that will take longer to humidify the next layer. Desiccant definitely helps scavenge water but you need to keep track of humidity because after a while the desiccant can collect enough water to start becoming a source.
Interesting. Is that what happens: Vapor leakage only depends on partial pressure difference and permeability of the foil. So as long as there is no water inside the bag, it doesn’t matter if there are other gases, that you would remove with the vacuum?
Yep. Exactly. As a gas, molecules don’t interact much with each other and behave like they are the only ones at the party. Increase pressure and that starts changing but at atmospheric pressure they are all mostly on their own. Kind of mind bending.
Thanks, there are a lot of interesting ideas and explanations. Up to this point I thought using any vacuum bag + desiccant + humidy readout = I’m good, no possible problems! But now I realise that I was fundamentally naive!
My initial thoughts are, yes, I agree that the inner filament possibly does contain some moisture, but shouldn’t the desiccant help? I tend to do overnight drying, so thats 10 - 14 hours drying time, also most double the typical 6 hour stints. But one thing to note is that the 6 month stored reel is at 43% which is exactly the same as the room’s humidity. So for now, I am going to assume that it is the plastic of the bags that is at fault. If it was 50+% then I might suspect moisture in the filament
I have done a bit of searching and have found three suppliers (so far) of bags specifically for storing filament, they all mention extra thickness and . One of which is Creality. I’m not sure which to try first. I cannot find any suitable mylar bags. To quote one of them Quote”Designed specifically for 3D printer filament, these 3D filament storage bags are stronger, tougher, more airtight, and more moisture resistant than ordinary food vacuum sealing bagsDesigned specifically for 3D printer filament, these 3D filament storage bags are stronger, tougher, more airtight, and more moisture resistant than ordinary food vacuum sealing bags.”Unquote.
Today, I opened some new filament. I measured the bags thickness it is 0.18mm. The bags that I am using are 0.085mm thick so about half the thickness. In the kitchen we also have a vacuum machine and Sous Vide bags the thickness is 0.16mm.
One question, how much desiccant is needed, new filament comes with a tiny desiccant bag. I’m using 50mg ATM.
That style of hygrometer samples air at the back of the unit.
If you’re mounting it inside the hole in the spool, then vacuuming the bag so the other side of the spool hole is also sealed, all you’re measuring is the humidity in the middle of the spool - NOT the filament.
The most accurate way to use that type of hygrometer is to put it in the bag loose, next to the filament.
@CarbonForge Thats a valid point. Actually, by chance I notice something. Look at the photo. The reel at 16% is the original humidy measuring style. The humidity unit is held by a round washer type shape, no ventilation. Whereas the 45% reel has a later “washer” design its much larger with spacers to keep the bag spaced away from the spool plus the slots allowing more air to circulate. So I must have thought about it!. But I take your point, and will revisit how best to get a valid humidity reading.
But you can be good with that setup. The thing is you need to be removing the water that leaks in by periodically regenerating/replacing the desiccant. The only thing that happens using plastic bags over thicker wall containers with lower leak rates is you have to regenerate or replace the beads more frequently. You can still keep your filament as dry as anyone else by keeping an eye on the hygrometers and regenerating/replacing the desiccant when the humidity in the bag gets too high.
As to how much desiccant to use, what using more gets you is capacity which can also affect humidity level as a byproduct. Humidity and moisture content can be related by curves. Different desiccants have their own curve determined by the structure of the desiccant at the molecular level. But as moisture content increases the humidity around the desiccant increases. Or as humidity increases, moisture content increases.
So using more desiccant means that the same amount of water becomes a smaller increase in moisture content and a smaller increase in humidity. It lets you soak up more water before the humidity rises to some level than if you used less desiccant.
Using more or less desiccant doesn’t really buy you anything except how long you can go between regenerating or replacing it.
The low cost hygrometer you’re using is a great instant reading of the conditions inside the bag, I use it on most of my spools in long term storage. However, I have also found that a moisture indicator card is a good gauge for determining “moisture over time”. Let’s face it, what the conditions inside the back at any moment is helpful but what we really want to know is how much humidity was present over time. For filament, that is more important.
So as an example, if I have a storage bag that reads 25% RH, that may not be an issue if the bag was in storage for let’s say 3 months. But what if I forgot how long it was there or the bag seal failed? Then that instant reading can’t tell me what the moisture history was, can it?
Here’s a search on Amazon. These are so cheap that one can treat them as disposable. But here’s a tip, I found that one can dry them with the filament in the dryer and they can be used multiple times, usually no more than 5-7 times in my experience.
Special Note Regarding Counterfeit Indicator Cards
Above all, when you get new indicator cards, test one sample. A good method is to include one with a damp paper towel inside a zip lock bag for 12 hours to ensure that what you received isn’t just inert ink. There are many counterfeit cards being shipped from Amazon. As an example, Elegoo has included counterfeit cards with their storage bags as I found out the hard way. They were just blue inert ink that did not react to any moisture. I asked them for a replacement cards and they sent me another shipment of storage bags with the same defective cards.
but how do those cards reflect history? In my experience, they change back their color when you put them in a dry environment again. Even the good ones you find in the packages for sensitive electronics.
That’s a great question. They do not record history in the way a data logger or an irreversible indicator does. A standard reversible humidity-indicator card shows the current relative humidity inside the container. Its indicator spots change color as the humidity rises and change back as the humidity falls.
The card therefore does not directly measure the moisture content of the filament or reveal precisely how long it has been exposed. It is simply a useful visual warning that conditions inside the container have become humid enough for the filament to begin absorbing moisture.
I use it as a conservative go/no-go indicator. If the 40% RH spot changes with something like PETG, I do not risk printing with it. I put the spool in the dryer first. Nylon is considerably more moisture-sensitive, so I use a lower threshold and dry it when the 20% RH spot changes.
The percentages indicate the relative humidity inside the container, not the percentage of moisture contained in the filament. As I stated at the outset, a digital hygrometer also shows only the conditions at that moment. It does not necessarily indicate how much moisture the spool has already absorbed.
Both the hygrometer and the moisture-indicator cards are useful tools, but each serves a different purpose.
as the main problem, but others have good thoughts re: the waters already in the roll to begin with.