Definition of absorb
1a : to take in (something, such as water) in a natural or gradual way
- a sponge absorbs water
- charcoal absorbs gas
- plant roots absorb water
Definition of adsorption
: the adhesion in an extremely thin layer of molecules (as of gases, solutes, or liquids) to the surfaces of solid bodies or liquids with which they are in contact
Some filaments will absorb moisture (PLA and nylon) and others will adsorb (ABS) moisture from the air. Of the two, absorption is a much bigger problem. If you've ever had PLA filament hiss and pop while it's being extruded, or crumble into pieces, it's because it absorbed moisture during improper storage. The result is a poor surface finish and often broken filament before it ever gets into the extruder.
Adsorption (what ABS does) isn't nearly as big a problem.
For those who demand a citation on this, I'm unable to locate one on the web. My info came directly from an engineer at Coex LLC who came to the Milwaukee Makerspace and made a presentation on plastics and how they manufacture their filaments. There used to be a copy of the presentation on their web site, but it doesn't seem to be there any more.
In general, it's a good idea to keep all filament cool, dry, out of sunlight, and covered so it doesn't accumulate dust and pet hair, etc. There are a lot of ways to accomplish all of this.
Some people use zip-lock bags or even vacuum bags that will seal the spools and keep them dust free. If you add some sort of desiccant, you can also keep them dry. This technique works fine but requires a desiccant pack for each bag.
I prefer large storage boxes because I can put multiple spools in each box, and one desiccant package per box keeps them all dry. The storage boxes I use have gasketed lids that help keep them sealed against intrusion of moist air.
When it comes to desiccants, there are a three common choices. Some people prefer silica gel, calcium chloride, or even molecular sieves. Silica gel is moderately expensive but can be reused by drying it in a low temperature oven for a few hours. Some even has chemical dye that provides an indication of when it has absorbed its limit of moisture.
Molecular sieves and their naturally occurring cousins, zeolite, work better than silica gel, but tend to be expensive. Like silica gel, some come with chemical dyes that indicate they are "full" and they too can be reused by drying in an oven.
In between silica gel and molecular sieves lies calcium chloride (CaCl2). It's cheaper than silica gel and zeolite, dries better than silica gel, but isn't readily reusable. In practice, that doesn't really matter- it works for so long the cost is negligible. Like silica gel, you can tell when it needs replacement because it absorbs so much moisture it literally turns into mud. Calcium chloride is sold under different brand names, the most common is DampRid.
Here's what I have been using for the last 3 years or so:
The box is a Sterilite 54 qt. weatherproof storage tote with a gasketed lid and multiple clamps to keep it sealed. There's a small tub of DampRid (lower left corner in the photo) that has been in the box and working for over 2 years (I replaced silica gel with DampRid 2 years ago) and has plenty of life left in it. The box costs about $10 and holds at least 10 spools of filament, and the DampRid comes in a 2 pack for <$5. It doesn't get much cheaper or more effective. I use one box for PLA/nylon and another for ABS.
You can buy this stuff almost anywhere. Walmart, amazon.com, Home Depot, etc. They all sell exactly this same stuff or the equivalent for about the same low cost.
Some people take this type of storage a step further and attach tubes to the boxes to feed the filament from the storage box to the printer. If you live in a very humid place that sort of thing may help prevent problems. I use filament up fast enough, and the climate here is dry enough, that the exposure to humid air that it gets while it's out of the box and on the printer hasn't caused any problems.