HOW TO STORE 3D PRINTER FILAMENT

Filament absorbs water from the surrounding air at a rate that depends on humidity and the specific material. PLA absorbs slowly (weeks to months); PETG faster (days to weeks); TPU faster again (hours to days); nylon and PC fastest (hours). Proper storage keeps filament at low humidity (under 20% RH) so absorption stops. Done well, a sealed spool stays print-ready for years. Done poorly, that same spool needs 6 hours of drying every time you want to use it - which adds up fast.

Always store sealed when: you've opened the manufacturer's bag and aren't planning to use the entire spool in one session. Most spools take days to weeks to print through; that's days to weeks of moisture absorption otherwise. Use a heated drybox when: you print nylon, PC, or other ultra-hygroscopic filaments regularly. They re-absorb fast enough that even sealed bags don't help between sessions. Don't bother sealing when: you'll print the whole spool in the next 24 hours and you're not running a hygroscopic material. Even then, why not seal it - takes 30 seconds.

Pick a storage system based on volume: 1. Vacuum-sealed bags (cheapest, best for occasional use): - Buy: vacuum-seal bags (food-storage type) and silica gel desiccant packets. - Place spool in bag with 1-2 desiccant packs. - Vacuum-seal. - Cost: ~$1 per spool. - Downside: slow to access (re-vacuum after each use). 2. Sealed totes / IRIS containers (best for many spools): - Buy: airtight tote (Sterilite, IRIS, etc.) sized for your spool count. - Add: 100-500 g of indicating silica gel desiccant in a breathable pouch. - Add: a hygrometer (cheap, $5-10) to monitor humidity inside. - Cost: $25-40 for a 6-spool setup. - Target humidity inside: under 15-20% RH. 3. Drybox (active or passive): - Passive: PolyBox, eSun eBox - sealed plastic with desiccant chamber and a filament feed port. Print directly from the box. - Active: PrintDry vault, Sunlu S4 - heated, holds 30-50C continuously, prevents and removes moisture. Best for nylon / PC. - Cost: $40-200. - Use when: you print frequently and want filament always print-ready, or you run hygroscopic materials. Desiccant management: - Indicating silica gel changes colour when saturated (orange-to-green or blue-to-pink depending on type). - Recharge by baking in the oven at 120C for 1 hour. Most desiccant can be recharged dozens of times. - Replace any desiccant that no longer changes colour back after baking - it's exhausted. Humidity target: - Below 20% RH inside the storage container. - Below 15% RH for nylon / PC. - Use a digital hygrometer to verify.

Skipping the desiccant. A sealed bag is only as dry as the air you sealed inside it. If your room is at 50% RH, the bag is at 50% RH until desiccant pulls the moisture out. Using table salt or rice as desiccant. They absorb very limited moisture. Use silica gel or molecular sieve specifically designed for moisture control. Forgetting to recharge desiccant. Once saturated, it stops absorbing. Bake in oven at 120C for 1 hour to renew. Storing nylon / PC in a vacuum bag and expecting it to stay dry for months. They re-absorb through any small leak. Use a heated drybox. No hygrometer. You can't manage what you can't measure. Cheap hygrometer eliminates guessing. Storing in the basement or garage. High-humidity environments overwhelm any storage system over time. Climate-controlled rooms are better.

Already-wet filament needs drying first - see how-to-dry-filament. Symptoms of wet filament in prints: how-to-identify-wet-filament and fix-wet-filament.