How dry do you store your filament?

I have this big plastic sealed box (normally used for food) and I threw in a bunch of silica pads/bags and a humidity meter (forgot the English name for these). In my room the humidity is around 40%. In the box it is just below 20%.

Anyone else know to what % they get? I still have plenty of room for adding silica and I have a kg of the stuff arriving soon, but I wonder how dry you can make a box like this with silica? What % is possible? For PLA and PETG this is more than sufficient, but if I would like to have any chance at storing opened PVA or nylon I would need to go a lot lower I think, if I don't want to dry the filament before use.