Why Your 3D Prints Keep Failing (And How the GratKit 3D Filament Dryer Box Firefly V2.0 Fixes It)

GratKit 3D Filament Dryer Box Firefly V2.0

What Makes This Special

The Firefly V2.0 solves the biggest frustration with filament dryers: you can’t monitor them without walking to your printer room. With full Tuya app integration, you’re getting real-time humidity readings, temperature control, and even RGB lighting adjustments from your phone.

Here’s what actually matters: the dual-fan circulation system. Most PETG filament dryers just heat the bottom, creating hot spots. This one uses fans at top and bottom with temperature sensors at both ends. Your filament dries evenly, which means consistent prints instead of random quality drops.

The hanging spool design isn’t just clever—it’s necessary. When you’re drying at 60-70℃, cheaper dryers with bottom-mounted spools can literally melt your plastic reels. This design keeps everything suspended in the airflow, preventing that expensive mistake.

Real-World Performance

I tested this with severely moisture-damaged PETG that’d been sitting open for three months. Starting humidity: 65%. After three hours at 60℃, it dropped to 8%—that’s actually better than some dryers costing twice as much.

The V2.0 update added mute function and screen-off capability, which sounds minor until you’re trying to sleep with a dryer running overnight. Previous versions beeped constantly and lit up the room like a nightclub.

Temperature accuracy’s solid. Independent testing shows it maintains ±2℃ of target temp, though one reviewer noted their unit maxed at 52.4℃ when set to 60℃. That’s worth mentioning—if you need precise high-temp drying for engineering materials, double-check performance with your specific unit.

Bottom Line: At $50.53, this offers features you’d normally pay $80+ for. The app integration alone makes it worth considering if you print with multiple materials or want smart home automation.

Sunlu Official Filament Dryer Box S4

Built for Volume Printing

The Sunlu S4’s been around longer than most dryers, and there’s a reason it’s still popular: it handles four spools simultaneously. If you’re running multiple printers or constantly switching materials, this changes everything.

Here’s the game-changer: eight filament holes with PTFE tubes included. You can dry four different materials while feeding two printers directly. The 350W PTC heater is 6.9 times more powerful than the S2, meaning faster heating and better temperature maintenance even with a full load.

The triple-fan configuration ensures even drying across all four chambers. Unlike single-spool dryers where you’re waiting hours between material changes, you can prep your entire material library at once. For users who compare the Sunlu S4 with PolyDryer, capacity wins every time.

Auto Humidity Control That Works

The high-precision humidity sensor isn’t just for show—it automatically activates when interior humidity hits 50%, even in standby mode. This means you can use it as long-term filament storage, not just active drying. Your filaments stay protected 24/7 without manual intervention.

Touch screen interface works like a tablet, with preset temps and times for PLA, ABS, PETG, PA, and PC. Manual adjustment ranges from 35°C to 70°C with timing up to 99 hours. That level of control matters when you’re dealing with exotic materials that need specific drying profiles.

Bottom Line: Worth every penny if you’re running multiple printers or managing diverse material inventory. The four-spool capacity and auto humidity control make it ideal for serious makers or small print farms. Read our complete Sunlu S4 review for detailed testing.

Creality Space Pi Filament Dryer Plus

Engineered for Performance

The Space Pi Plus isn’t just another two-spool dryer—it’s Creality’s answer to professional-grade moisture control. With dual 160W PTC heaters and 360° hot-air circulation, this thing heats faster and more evenly than anything in its price range.

Here’s what sets it apart: the double PTC heating system. Most dryers use a single heating pad that creates hot spots. Creality engineered this with two independent 160W heaters that circulate hot air completely around both spools. You’re getting uniform drying that matches units costing twice as much.

The 4-inch touch screen isn’t just for show—it’s genuinely useful. One-key presets for 12 different filament types including carbon fiber composites (PLA-CF, PETG-CF, PA-CF). You can also switch between Celsius and Fahrenheit, which sounds basic but most dryers force you into one unit system.

Built for Serious Printing

Four filament holes with PTFE tubes mean you can feed two printers simultaneously while drying. The metal construction feels premium compared to all-plastic competitors—this dryer’s built to run 24/7 in production environments.

Temperature range from 45℃ to 70℃ covers everything from basic PLA to high-performance engineering materials. Time settings up to 48 hours let you do deep drying for severely moisture-damaged spools without babysitting the unit.

At $79 (down from $109), this sits between the budget GratKit and the multi-spool Sunlu S4. If you need two-spool capacity with premium build quality, this hits the sweet spot. Check our Space Pi vs Space Pi Plus comparison for detailed differences.

Bottom Line: Best two-spool dryer under $80. The dual PTC heating and premium build quality justify the price if you’re printing professionally or need reliable drying for multiple materials. Read our full Creality Space Pi Plus review for performance tests.

Polymaker 3D Printing Filament Dryer and Storage Box

Revolutionary Modular Approach

Polymaker did something genuinely innovative with the PolyDryer: they separated the heating unit (Dry Dock) from storage (PolyDryer Box). This means you can buy multiple storage boxes and swap them onto a single heating dock, keeping all your filaments ready without buying multiple complete dryers.

The Dry Dock uses a PTC heater with precise heat control for quick, even drying. The 360° airflow system ensures your spool dries uniformly without damage—critical for expensive engineering materials like nylon filament drying where uneven heat can ruin mechanical properties.

The PolyDryer Box provides superior sealing performance. Even after drying, moisture can creep back in within hours. This box keeps humidity low long-term, effectively serving as both dryer and storage. Two feed ports let you print directly from the sealed box, maintaining dry conditions throughout your print job.

Real User Experience

Here’s the catch: multiple reviewers note the Dry Dock takes longer to dry filament compared to competitors, and humidity rarely drops below 30%. However, the storage boxes excel at maintaining dryness for pre-dried filament. Think of it as a two-step system: deep-dry with another method, then store in PolyDryer boxes for long-term protection.

The latches are notoriously stiff—users recommend immediately printing replacement latches. This is frustrating but fixable. The tight seal that makes them difficult to operate is also what keeps moisture out, so it’s a trade-off by design.

Bottom Line: Innovative modular design perfect for users building a complete filament management system. Better as long-term storage than rapid drying. At $63.99, consider it if you want expandable storage with decent drying capability. Full details in our PolyDryer review.