The Sunlu S2 filament dryer does not have active ventilation, therefore the filament moisture accumulates inside the dryer. The modular spacer allows greater ventilation and allows more efficient extraction of moisture.
The spacer is adjustable from 6mm up to 30mm.

I recommend printing it with the most heat resistant filament that you want to dry inside. PLA could soften when drying PETG or other filaments that require high temperatures.