This is a silica gel box which can be clipped on the side of the spool to keep your filament dry. It should work with almost all 1kg spools.

Print instructions

To make the bottom and top permeable to air I did the following:

Using Slic3r:

-Load the body.stl and mesh.stl
-Don't change orientation of the parts yet
-rightclick on body->Settings->Load modifier->select the body_mod.stl
-select the body_mod.stl
-click on the green plus sign
-select:
Infill->Fill density: 70% (maybe less)
Infill->Fill pattern: Grid
Layers and Perimeters->Bottom solid layers: 0
Layers and Perimeters->Top solid layers: 0