It is a well-known fact that some 3D printing filaments are hygroscopic (they absorb moisture from the air). For some (like ABS) this is noticeable but you can still produce usable prints. Nylons on the other hand become completely useless for printing after even just a few hours out in the open.
Since I am experimenting with flexible filaments, including nylons, it was necessary for me to have a drybox. I made one using a large plastic box from Walmart. I added a humidity gauge and filled it with 5lb of silica. For really sensitive filaments I have a small hole in the box, so I can print without even taking out the filament.