How wet is new 3d printer filament? Measuring dry box moisture

You all had questions, I now have answers! Comments from my last filament storage video mentioned using a hygrometer to measure humidity levels. So I picked up some smart hygrometers, and ran a series of experiments to see how well to dry boxes really work.

SwitchBot 4-pack Smart Hygrometer/Thermometer:

46qt Storage bin:

Eva-Dry Dehumidifier:


Hey everyone and welcome back to Hoffman Engineering. In my last video we made some more filament dry storage boxes, using sealed 44 quart containers and renewable dehumidifiers. There were some great comments about measuring moisture levels, so I thought I’d run some experiments to see if dry boxes like this even do anything.

I wanted to answer a few basic questions:

  1. What is the humidity inside the boxes kept at?
  2. How does opening the box affect the humidity?
  3. Is the filament inside factory sealed bags already dry?

To test, I purchased a four-pack of SwitchBot Wireless Themometer and Hygrometers [Not sponsored, they were just good value on Amazon]. These are bluetooth enabled smart sensors, which record temperature and humidity levels. The data can be viewed within their app, or downloaded as csv files. After unpacking them and pairing them with the app, I checked that they all reported roughly the same values in my office. Great. My office appears to keep around 40-43% humidity, so that will be my baseline.

I purchased 4 of the sensors. One will be placed in the open air in my office to track the baseline values. The others will be placed in my 3 filament storage boxes. Each box is filled with rolls of filament, and an Eva Dry renewable dehumidifier. 

And as expected, 18 hours later, the humidity levels has dropped substantially. Box 3, with the brand-new dehumidifier, dropped from 42% humidity to 27% humidity within about 4 hours. However, Box 1 and Box 2 were only at 36% humidity.

This was an indication that those dehumidifiers weren’t entirely dry. I took them out of the boxes and looked at the beads. Box 1’s was reporting mostly dry, but the older-style colored beads for Box 2 was harder to read. I decided to plug them in and dry both of them for 12 hours overnight.

And that made a world of difference. After drying 12 hours, Box 1’s beads look almost the same, but box 2’s beads are now very blue. So I placed them back in their boxes. Another 12 hours later, we can see that Box 1 has dropped from 36% humidity down to 28%, about the same as Box 3. Box 2 has dropped from 36% down to only 33%, but that makes sense because box 2 is a 70 quart box, which is much larger than the 44 quarts of box 1 and 3.

Flash forward a week, and the smaller box 1 and 3 are down to 23% humidity. It took about 4 days to reach this level. I would expect it to drop another couple of percent, but it has dramatically slowed from here. So to answer Question #1, these dehumidifiers will keep the 44-quart filament boxes at around 23% humidity. Box 2, the 70-quart box, seems to have stabilized at 28% humidity.

So on to Question 2:

How does opening the boxes affect the humidity? I briefly opened box 1, for roughly the amount of time needed to grab a roll of filament. 12 hours later, I checked on it, and saw that it jumped up to 36% humidity, but within 4 hours it was back down to 28% humidity. So I can say that while briefly opening the container does cause humidity levels to spike, the dehumidifiers are able to handle it within a few hours.

And now the most interesting question. In my filament storage video, I originally said you can keep the filament in the bags, or open them now, it shouldn’t make a difference if they have dissicent in them. However, user D-railed left a comment recommending to open the bags, since you can’t be 100% sure they are actually dry inside. So lets test that.

I took box 3, and removed all the rolls from their bags. Each bag was still nicely vacuum sealed, and there was a packet of desiccant in each. After removing all the bags, the humidity matched the office air at 38% percent.

Then what happened was very interesting. Starting from when I unbagged them Saturday morning, moisture levels initially dropped quickly, but then stayed at 33% for the next 2 days. This indicated that the dehumidifier needed to be dried. So Monday morning I dried it, and put it back in. From Monday morning to Thursday night, humidity levels slowly dropped from 33% to 25%. This was much slower than expected. Remember that our answer to Question #2 was that it took 4 hours to dry the air from opening the box, not 4 days. I could think of 2 possibilities: either A) it took longer for me to unpack the filament, so the box was open for longer, allowing more air to be exchanged and taking 4 days to dry. Or b) the filament was not dry, and slowly gave up extra moisture over the 4 days.

To test, I simply opened the box again and made sure the air was fully exchanged. I kept it open for a couple of minutes, using the lid as a fan to blow air into it, making sure it was filled with ambient air. Looking at the data, we see the initial spike on Thursday night , but then it quickly dropped back down to the 25% over the span of about 4 hours. This matches the 4 hours we saw before, and indicates that it was the filament that was slowly drying over the last 4 days. This means the filament in their bags wasn’t dry, and it takes a number of days for the filament to give off extra moisture.

So lets summarize what we’ve learned:

  1. The dehumidifiers inside of dry boxes keep the humidity level around 23%
  2. 2 Opening the box causes the humidity level to climb back to ambient levels, but recover after about 4 hours.
  3. 3. Sealed filament is not reliably dry, at least above the 23% humidity of the dry boxes. If you get a new roll of filament, you should open it before placing in your dry box, just to make sure it has time to dry out.

So thank you for geeking out with data with me. This experimentation was fun, and it all started from comments from you. So if you have any more questions about filament and moisture, please leave them in the comments below. I’d love to revisit and experiment more with filament moisture levels in the future. So thank you all for watching, and I’ll see you all next time.

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