Building a 3D Filament Dry Box with Active Control

Moisture-absorbed PLA and PETG filament stringers badly and causes brittle prints. A properly controlled dry box solves this.

The enclosure is a Pelican-style airtight case with desiccant packs. The active element: a DHT22 measures relative humidity inside the box; an Arduino triggers a small 5V resistive heater element when humidity exceeds 15% RH. The heater drives moisture out of the desiccant and the filament.

Target: maintain the interior below 15% RH. At 10% RH, PLA can be stored indefinitely without moisture absorption. The heater cycles about 3 times per hour and draws about 10W when active. A 12V laptop supply powers the whole system. I've been running it for 8 months and the filament quality is noticeably better — no more stringing on bridges.