Spoiler alert: The best technique isn’t in this article, that’s for part 2. Assuming my theory is right. I guess we’ll find out when we get there!
I 3D print a lot, and often with unusual engineering filaments a bit more hygroscopic than the usual PLA and ABS/ASA – things like nylon, polycarbonate, TPU, and so on. Even the basics, PLA and VERY much PETG print much better when they’re dry, and even though PLA isn’t very hygroscopic, it will still pick up moisture over long periods especially when stored in a place like my very humid garage. So all this to say, proper moisture-controlled filament storage is important to me, so I don’t have to spend hours waiting for filament to dry every time I break from my daily driver spools.
Up until now, I’ve used two techniques to store spools, each with their pros and cons. The first involves a “weatherproof” storage tote, with a lid that seals mostly-airtight. Fill the bottom up with a bunch of loose desiccant and then the rest with spools, and you’ve got a bucket that’ll keep the contents nice and dry.
It actually works quite well. This is a month of data and it’s been quite a few months since I last dried the desiccant and the spools in this bin. You can see that the spikes caused by me opening the bin get absorbed again by the desiccant very quickly, and don’t make much of an impact on the average baseline humidity before vs after. Note: the oscillation is because the temperature in my garage changes over the course of a day. When it gets hot, relative humidity drops, when it gets cold, it goes up, since moisture isn’t really moving much.
Aside: (That’s actually not totally true. If it were temperature and humidity would be 180 degrees out of phase where a temperature peak is a humidity valley. Instead, they’re about 90 degrees out of phase with some distortion. I suspect this is because at a certain point the heat starts driving moisture out of the desiccant, then when the air cools and the RH increases, the desiccant re-adsorbs that moisture.)
Anyway I digress.
This method generally works, but it’s not THAT sustainable. The overall moisture setpoint of the box increases over time, and faster the more you access filaments in the box. When the desiccant is finally spent, you’ve got a TON of it to dry all at once, and potentially 8+ spools at the same time if it went too long. In a perfect world, you’d ONLY expose a roll to moisture when you actually wanted to print it, so you’d only have to dry it a couple times in its life before you’ve printed it all. With the box, you might have to dry a spool a couple times without ever printing it once.
The second technique is pretty common among 3D printers, which is to use vacuum bags designed for sous vide cooking. The idea is that by bagging your spool then pulling a vacuum on it, you 1) block out moisture in the ambient air 2) remove any moisture that you might have stored in the bag with the filament (by removing the air) and 3) give yourself a ready indicator if that barrier gets breached (if the bag leaks and is full of air when you get back to it, you know it broke). Some people thing there’s a 4th benefit, which is that the vacuum is actually sucking moisture out of your filament. Maybe the slightest little bit, but CNC Kitchen ran some experiments on this and the conclusion is that pulling even a very strong vacuum on filament isn’t nearly as good at removing moisture content as heating it, and his vacuum was much stronger (~14.7psi) than what you get with sous vide bags (maybe like 5psi).
When I do bag filament I like to put both desiccant and a humidity indicator strip in there. Lots of my desiccant packs are color-changing. The other day I noticed something interesting, which is that some of my bags were bone-dry according to the indicators, while others looked nearly ambient humidity.
I thought I had a problem with some bags being more moisture-permeable than others, but I ran some experiments with the same moisture indicators across the two or three different brands I had and they all showed lots of humidity after only a day or two. Then it finally clicked for me when I realized that I had a color-changing desiccant pack in a bag like the one on the right above – the desiccant was indicating “very wet” while the indicator paper was indicating “0%” – It turns out, I have a bad batch of humidity indicators! Unfortunately, this also means that all of my sous vide bags also kind of suck at blocking moisture. Or like, totally suck.
Now, some filaments come packed in similar-looking, if slightly heavier/thicker, clear polyester vacuum bags. but lots of spools, including one I happened to open two days ago from Polymaker, come in metallized bags. Which got me thinking it’s about time for another experiment!
More on this in Part 2, but the results are already interesting!
Be First to Comment