Hello.
I am making a few drying boxes for my filament. I keep my printer and supplies downstairs. Now, it is a bit cooler down there. Does that make a difference? Will the silica desiccated still dry it to what I need, or should I be storing the used filament upstairs?
*Note: I live in central Ontario, Canada, so the temperature today is 17° celsious, 62 Fahrenheit.
To answer your question. Don’t overthink this problem. Learn how to measure humidity and get some desiccant. Silica gel is all you need and above all, don’t get caught up in all the hype in this and other forums. It’s a simple equation. You have moist air and you want to make it dry. There are two ways to achieve this. Passive drying(Sealed container and desiccant) and active drying(using heat).
Have a look around the forum and use the search feature for the subject drying and you will be rewarded - or punished - with a plethora of good and bad information. You have to educate yourself as to which you can trust.
Did I mentioned “Don’t over think this?” If not, here are the two rules. 
Here are a couple of really active topics. Some at my own hand, so even the person giving you this advice can be guilty. 
Well, that sums it up! I just wanted to be sure. When I do a google search, I get into a rabbit hole, and can’t find a definite answer. My desiccant just arrived now, as well as my hygrometers.
Appreciate the helpful advice.
Cheers
The one hint I might add is if you don’t already have one, get yourself a cheap kitchen scale. Weigh the filaments spools upon opening and what I liked to do is right the weight right onto the spool. I also weigh it when the spool is empty and keep a spreadsheet of tare weights for future use. Note that paper spools themselves can contain moisture.
The other thing to do is weigh your desiccant. Most manufacturers will list a percentage of water absorption. The easy thing to remember is that 1gm=1cc=1ml of water. So calculating percentages is remarkably easy. I fact, if you don’t get the color changing silica gel, weight is really the only way to know if your silica has to be dried out again. This also works on other rechargeable desiccants such as clay or even table salt(it’s what’s in Bambu desiccant bags).
By actually weighing for yourself, you escape the rabbit hole of opinions because you are the one applying your own measurements rather than the ubiquitous Internet opinions of “… well it should…” or my personal favorite “… I would have to believe…”.
Here’s a list I found on the web that lists the absorption % by weight of common desiccants.
| Desiccant Material | Moisture Absorption (% of Weight) |
|---|---|
| Silica Gel | 40 |
| Activated Alumina | 20 |
| Molecular Sieves | 22 |
| Calcium Chloride | 200 |
| Montmorillonite Clay | 25 |
That’s actually a good idea. I never thought about the spools themselves holding moister. How often should I be changing the silica gel?
Side question: Why do people print spools and re-spool their filament?
I assume the most common reason, for Bambu users anyway, is third party spools that are not compatible with the AMS.
Ah. Makes sense. Thanks. Thought maybe it was to make it look nicer or something.
Changing your silica is something you can easily monitor so there is no fast rule. It’s kind of like, when does an air freshener need changing? Answer: When it’s used up. A hygrometer that you pack in with the filament can be very handy and cheap. In bulck they can go for as little as $0.50 and in pairs they are about three bucks. They come in rectangular and circular. The thing you want to watch for is that some display both C and F temps while some do not. All display RH%.
Here’s a link on Amazon
Note: These are all the same design. The are like disposable pens. Their initial purpose was for Cigar Humidors.
For me they are so cheap, I tend to toss them in a storage bag with desiccant for those small spools like in the case TPU, that I don’t use a lot of. Note the use of the moisture indicator card. The two devices perform slightly different functions. Hygrometers give you near instantaneous readings whereas moisture cards give you total absorption over time. What’s nice is that the moisture cards can be renewed by placing them in the same drying method that one uses for drying silica gel. Early on, I used my kitchen oven before my wife started to complain. Moisture cards come in a variety of styles. Here is a link to Amazon. As is with all things like this don’t get sucked into the vortex of spin, like hygrometers, buy on price.
The only warning I might give is to test them out of the box. There are a ton of counterfeit moisture indicator cards on Amazon, some from reputable companies like Amogen that they include in their purpose-made vacuum bags. Take a card, and put it in a steam bath and cover it. It should change in 5 minutes. If not, what you got is a card with just ink. As was the case here:
Here’s an exampled where I employed for a 200g spool. Note the “Super Advanced” packaging that I employed from that super high tech company “Glad Sandwich Bags”. 
Point is, you can get really carried away with purpose-made products when you likely already have most of the stuff you need either in your kitchen, basement or attic. It’s one of my pet peeves when I see something labeled “Formulated for…” and then I find out, it’s mostly H²O and some other household ingredient I could get for $0.50.
The dominant reason for respooling is to allow another manufacturers filament to be respooled onto a Bambu spool thus making it easier to feed in a Bambu AMS.
I would be careful with the 50 ct hygrometers.
I bought a pack of 10 and after laying on the desk for a day, they showed everything between 40 and 60%. I don’t believe it will be better at the low end of the measuring scale.
Olias, wasn’t you the one who proposed to me those Bluetooth sensors from AliExpress? I now have a bunch of those: https://a.aliexpress.com/_Evk9cVN
I got them for 1,79€, seems they cost a bit more now.
They were all within ±2% also with a different more expensive sensor.
I also ordered two different zigbee versions, but they both had some flaws, so i didn’t see a reason to spent the extra money.
One of them went into the AMS, some into filament bags and some are spare.
I also added a tuya Bluetooth bridge for 8€. Now I can look up the humidity in the Tuya app without taking the filament out of the cabinet. With the bridge, you can even setup an alarm when humidity rises above a threshold, so you know that you have to exchange the dessicant in the AMS or one of the filament bags.
It is still quite cost effective and it took me maybe an hour to set everything up, including tinkering.
I’m quite happy with that now. Especially that I don’t need to check anything regularly but get informed when I need to take actions.
Definitely not me.
On the subject of cheap hygrometers though. They have an RH range of 10-90% and use the exact same components that are found in everything from high end dehumidifiers to thermopro household thermometers to cheap and expensive filament dryers. So there is little to know difference between the technology, just price.
I have to disagree. The sensor I proposed has a range of 0% - 99%, so apparently they don’t use the same components internally.
Actually there is a wide array of different sensor components available. Sensirion alone, a well regarded manufacturer of environmental sensors, sells more than 50 different types of humidity sensors, all with different specifications.
And my first hand test of 10 of those cheap hygrometers showed a spread of 20% after settling for more than 24 hours, while 8 of those bluetooth sensors all where within 4% of each other. No idea, which components each of them use, but in direct comparison, my experience was much better with the bluetooth sensors.
Here PAHT-CF cannot get dry anymore? - #14 by Dragster43 somebody made the same experience as me with the cheap sensors.
Yes, I recall that post, but I think the OP makes a fair point but has some truly unrealistic expectations of this device. That’s why these are so cheap; they are like BIC pens—when they stop working correctly, you throw them away.
Whenever I open up a box of these cheap hygrometers, before I use them I run a simple salt-brine calibration test. None of these are accurate to more than ±3% in my experience. But we aren’t talking about laboratory-grade equipment either. One has to "Calibrate"
one’s expectations, doesn’t one?
Here’s a very simply search on YouTube, there are so many videos on how to check your hygrometer. All you need is table salt, water and a sealed container.
https://www.youtube.com/results?search_query=calibrating+hygrometer
BTW: I don’t even trust my Creality dryer sensor either which is why I keep a second sensor in the box just to keep the readings honest. The Creality Sensor is close enough or as the Chinese prefer to say, chà bù duō, which explains everything about products sourced in China from Chinese engineers.
I know that when I open a drybox to remove filament, the filament isn’t going to instantly absorb moisture, (obviously), but how long does it take filament to absorb moisture to the point where it needs to be resealed?
Wow! If no way to calibrate, that’s all but useless. I guess the best you can do is throw out the bad ones and track the remaining ones to see whether or not they also go bad over time.
I never use a hygrometer and thus save myself too much thinking, so I basically follow rule no. 1 
I think that is an anomalous experience. I would have returned those to Amazon if that were my experience. I’ve never had that far a variance with over 20 of these devices both cheap and expensive. Like I said ±3% but for the purposes of determining moisture content, I think we’ve all beat that one to death, before and after drying weight is the one measurement that will give a good indication of how much moisture was present. After that, it comes down to monitoring how much is present in the environment that the product is stored in. This is another reason I use moisture indicator cards. I’m not using them for accuracy but rather for just what they are, indicators. If I see most of the blue circles change color, I place the spool along with the desiccant and the moisture card back in the dryer and I weigh before an after. So far, even when the cards go completely pink, there hasn’t been a substantial difference in dry weight after I’ve taken a once-dry spool and dried it a second time after I take it out of the container/bag that had desiccant in it.
I agree. 3% or even more would be perfectly fine for me but 20% is just too much. I don’t want to spend the effort and time to check each one individually. Of course your mileage may vary.
Anyway, I just wanted to propose an alternative, that might be interesting for the OP.
Lots to learn. I really appreciate the helpful information from everyone. I DO want to weigh my filament when it arrives today, and then weigh it a few days later and see the difference. I noticed last night, that my TPU was hissing and popping while printing, which hasn’t happened before, and was really stringy. Might weight that now and then weigh it later to see the difference. 
That my friend, is a classic sign of moisture and TPU is known for being hydroscopic. Place the spool in your oven for 3 hours at temps not to exceed 50C or 150F for 4 hours, or 8 if you can and you will see a world of difference. Or you can simply place it on your heat bed with the cardboard carton that the filament came in for the same period of time and set the bed to 50C or just use the bed drying feature if you have an X1.
