This Is Why They Talk About Drying Your Filament

I went to start up a print today and loaded an old half-full spool of black PETG into the printer. I ran the filament through the nozzle to purge what was left of the previous filament and, as the white plastic faded to grey and then black, I heard an odd ticking sound coming from the nozzle.

I store my filament in zipper bags with a pack or two of desiccant, but even with those precautions, it only slows moisture down – it doesn’t stop it. It’ll make its way in through any tiny hole in the plastic, and water molecules can slowly make their way between the molecules of the plastic bag. You can’t see it or feel, it but with enough time and the right conditions, it’s enough to saturate the desiccant and start working its way into the filament.

In this case, the bag containing the filament spool had been sitting long enough and had gone through enough temperature/moisture cycles (I store it in the basement) that the filament had absorbed some moisture. The moisture was evaporating and creating bubbles and little pops in the plastic as it went through the nozzle at about 220° Celsius:

Bubbled Filament
You can easily see and feel the bubbles even though the diameter of the filament is only 1.75mm.

If I really wanted to, I could probably still print with it, but the printed surface will probably be rough and adhesion wouldn’t be as good.

Fortunately, drying filament is pretty simple. Machines dedicated to drying filament are available, and while they have trays and covers made to fit filament spools, I found them to be a bit too expensive for my budget. I ended up buying a cheap food dehydrator from my local hardware store and drilling a couple of holes in an old Tupperware container to use as a lid:

Now I just need to let it sit for a while and the filament will be good to go!

2 thoughts on “This Is Why They Talk About Drying Your Filament”

  1. bought the exact same dehydrator. some people are saying the temp isn’t accurate so best to keep an eye on it. what container exactly did you use for cover?

    1. Hi, sorry it took me so long to reply…

      You’ve got a very good point. I check it about every half hour when it’s running – just doing the back-of-the-hand thing. You’ve got me wondering now, though – I should toss a thermometer in there and see how it compares to the dial.

      The container is a Rubbermaid 1.6gal/6.0l. It also has “401A 1” on the bottom, not sure if that’s a model# or useful at all. It works pretty well, although I had to tape up the indents around the rim.

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