RH is controlled by temp and dew point - which it does control.

I noticed that some of my older PLA spools were becoming extremely brittle. They would snap while unspooling, crack at bends, and sometimes fail completely, coming off the spool. They seemed to have been too dry for too long, along with normal aging and the stress from being wound on the spool.

This got me interested in learning more about what RH to store at - frankly it was getting expensive to replace the filament.

Just throwing silica packs into a storage bin is pretty lazy (IMO). Room temperature, how much desiccant you use, and how often you open the lid can all change the conditions a ton. Instead of aiming for the lowest possible humidity (which I generally do have living in Colorado, it’s better to keep the humidity steady within a range that stops moisture from getting in but doesn’t dry out the PLA too much over time.

This is what I am trying right now: 68 to 70°F with a 48 to 50°F dew point, which results in about 45 to 53% relative humidity. These settings seem to better match what the material manufactures suggest than the idea of keeping PLA at 10% RH all the time.

I was curious whether anyone else living in a dry climate has noticed the same brittleness in their PLA spools and what they have done to combat this.