We designed a 3D printer in Grenoble’s Hackerspace (France), which works really well thanks to its stiffness. Nevertheless, I had some troubles regarding PLA humidity: there are bubbles at the nozzle outlet when it absorbs too much moisture. So I found that:

• PLA might arrive from supplier with moisture, I had the case for a RepRap World neutral PLA
• Some PLA are more sensitive than others to humidity, and it seems to depend on the color. The following list is a feeling, from most to less sensitive
  1. Colorfabb red, green
  2. Colorfabb grey
  3. RepRap World neutral
  4. Paoparts (not the premium)
  5. Faberdashery, any color seems to be not sensitive…
• As written on the Internet, 40°C in the oven for few hours is great to dry the filament

For most people, keeping the PLA in a sealed box when not in use + drying it from time to time is enough. But I found that Colorfabb PLA is absorbing moisture in 3 or 4 days in my office when loaded on the printer, also, I think that it can have long term effects on PLA to dry it too many times in the oven.
So I investigate how to keep it dry, and if my storage box is really sealed; I used my sensors from NoteRF project.

• My storage box was not fully sealed, so I used sealed bags instead: the same you can use with a vacuum to store clothes.
• I was using small bags of Montmorillonite clay as desiccant, but it is not really useful.
• Silica gel is really better, I use the variation which is orange when dry and green when it absorbed moisture.
• Drops relative humidity from 45% to 23% in less than 1 hour @21°C.
• Can be regenerated in the oven faster than PLA, without long term degradation.
• I observed that there is natural PLA desorption: after a few days the relative humidity inside the bag did not change but silica was green. I changed it, the same phenomena appeared again after 2 weeks. Now, it seems that the silica is not turning green… And the PLA prints well, which was not the case before.

The next step is to make a box to keep it dry while used, but this storage with desorption significantly reduce my problems, and my PLA is currently stored at 17.5% RH (20°C) :

To hold the silica, I designed a customizable box in OpenSCAD, available on Thingiverse.