SUNLU FilaDryer S2
The SUNLU FilaDryer S2 is a $45 single-spool heated filament dryer with hot-air convection, an LED display, a 0-24 hour timer, and a temperature range of 35-70°C. A PTFE passthrough port lets you print directly from the dryer, keeping moisture-sensitive filaments like nylon, PA-CF, and PETG dry during long prints.
The right $45 filament dryer for one spool at a time — step up to the S4 if you swap colors often.
Where to Buy
Pros
- $45 puts active filament drying in reach of every hobbyist printer
- 35-70°C range and 0-24 hour timer cover PLA, PETG, ABS, and nylon dry profiles
- PTFE passthrough port enables print-while-drying for long jobs in humid climates
- Fits any 1.75mm or 2.85mm spool up to 1kg / 200mm diameter — brand-agnostic
- Universal 100-240V input with ~35dB noise level is quiet enough for office use
Cons
- Only one spool at a time — multi-color setups need multiple S2 units or the S4
- 70°C ceiling means PEEK and ULTEM (which need 100°C+) won't dry properly
- Single-direction airflow leaves the bottom of the spool less dry than the top
Why Filament Drying Matters More Than You Think
Filament absorbs moisture from the air at rates that depend on the polymer chemistry. PLA absorbs slowly (weeks to noticeable problems), PETG faster (24-48 hours in humid air), and nylon almost instantly (hours). The absorbed water turns to steam in the hotend during printing, exiting as small bubbles that disrupt the extruded line. The visible signs are popping or hissing sounds at the nozzle, stringing between perimeters, matte or fuzzy surfaces, and weak interlayer adhesion. Dry filament prints with crisp lines and a smooth shine; wet filament prints look tired and underextruded.
A properly dried spool isn't just visually better — it's mechanically stronger. Wet PETG prints can have 30-40% lower interlayer strength than dry PETG, turning what should be a tough functional part into a brittle prototype. For engineering applications (printer mounts, mechanical fixtures, enclosures under load), filament moisture content is a make-or-break variable. The S2 lets you guarantee dry filament before printing instead of hoping the spool stayed dry on the shelf.
Dry storage matters too. After drying, the filament needs to stay dry. Vacuum-sealed bags with desiccant work; ambient room storage doesn't. The S2's PTFE passthrough port enables a different strategy: keep the spool in the dryer permanently and print directly from it. This eliminates the storage problem entirely — the filament you're printing was just dried hours before. For nylon and PA-CF in humid climates, this is the only reliable approach.
Print-While-Drying: The PTFE Passthrough
The S2's most important feature is the PTFE passthrough port that lets filament feed from the spool inside the heated dryer through a tube to the printer's extruder, with the dryer running the entire time. This isn't a niche feature — it's essential for nylon and PA-CF, where filament absorbs moisture faster than most prints complete. A 6-hour nylon print without active drying often shows progressively worse layer adhesion as the spool sits in ambient humidity during the print; with the S2 keeping the spool at 70°C the whole time, layer quality stays consistent end-to-end.
Setup is simple: thread the PTFE tube from the dryer port to the printer's extruder, ensuring the tube is free of sharp bends. The tube adds a small amount of friction to the filament path, which most extruders handle without trouble. Bowden-style printers with already-long filament paths see the most additional friction — some flexible filaments (TPU 95A and softer) may have feeding issues with a long passthrough run. For direct-drive printers, the passthrough adds negligible friction.
The passthrough also enables a clean dry-storage pattern: keep an S2 running 24/7 at 40°C with whatever filament is currently in use. Each fresh spool gets dried at its proper temperature on first load (4-8 hours), then the S2 holds dry conditions for as long as the spool lasts. At 40°C maintenance temperature the S2 draws roughly 15W — about $1.50 per month in electricity. For a printer running multiple times a week, this is the cheapest insurance against wet-filament print failures.
Temperature Profiles and Material Limitations
The S2 covers 35-70°C, which fits most consumer filaments. PLA dries at 45-55°C / 4-6 hours; PETG at 60-65°C / 4-6 hours; ABS at 65-70°C / 4-6 hours; nylon and PA-CF at 70°C / 8-12 hours. The 0-24 hour timer covers all of these with margin. The display shows current chamber temperature and remaining timer in minutes. The hot-air convection design heats the spool relatively evenly, though the top of the spool dries slightly faster than the bottom because warm air rises — rotating the spool 180° halfway through drying gives the most uniform result.
The 70°C ceiling is the S2's main limitation. PEEK and ULTEM (high-performance engineering polymers) require drying at 120-150°C to remove moisture; the S2 can't reach those temperatures. Polycarbonate dries reliably at 80-90°C, which is also above the S2's range — you can dry PC at 70°C for longer (16-24 hours) but the result is worse than at the proper temperature. For PEEK, ULTEM, and to a lesser extent PC, the PolyDryer Box (130°C max) or a dedicated industrial filament oven is the right tool.
For TPU, the rules are different: too much heat can cause TPU to soften and stick to itself or deform on the spool. SUNLU recommends 50°C / 4-6 hours for TPU 95A, well within the S2's range. Softer TPU (85A, 90A) is risky to dry because the lower softening point overlaps with effective drying temperatures — dry these at 45°C for longer (8-12 hours) and check periodically for spool deformation.
Common Gotchas
The S2 holds one spool only. Multi-color setups need a separate dryer per active color, or a step-up to the SUNLU S4 ($130, 4 spools). Multi-color users routinely buy 2-3 S2 units, which adds up to nearly the price of an S4 — worth doing the math before stacking S2s.
The 70°C maximum cannot dry PEEK, ULTEM, or even properly handle polycarbonate. If you print high-temp engineering polymers, the S2 is undersized. Buyers print PC at 70°C and find the prints still show moisture symptoms because the filament isn't fully dried. Read your filament manufacturer's drying recommendation before buying — if it's above 70°C, the S2 isn't your dryer.
Airflow is single-direction (top-down). The top of the spool dries first; the bottom takes hours longer. For thorough drying of a fresh wet spool, rotate the spool 180° halfway through the drying cycle. SUNLU's documentation doesn't emphasize this but it makes a real difference for nylon and PA-CF.
The PTFE passthrough adds friction to the filament path. Most direct-drive printers handle this fine. Bowden-style printers with already-long filament paths sometimes have feeding issues with very flexible TPU when adding the passthrough — the cumulative friction overcomes the extruder's grip. If you print soft TPU (85A or 90A), bypass the dryer for those prints.
Condensation builds up on the lid during drying. As moisture evaporates from the filament it has to go somewhere, and a cool lid is where it condenses. The droplets can drip back onto the filament if the lid isn't periodically wiped. Crack the lid open every 2-3 hours during long drying cycles to vent the moisture — a simple step that SUNLU mentions in fine print but most users skip.
Full Specifications
I/O & Interfaces
| Specification | Value |
|---|---|
| Display | LED display with temperature and timer |
Power
| Specification | Value |
|---|---|
| Input Voltage | 100-240V AC, 50/60Hz (universal) |
| power_consumption | 48W max |
Physical
| Specification | Value |
|---|---|
| capacity | 1 spool (up to 1kg, 200x200mm diameter) |
| Dimensions | 265 x 245 x 175 mm |
| weight_g | 1900 g |
Who Should Buy This
PETG absorbs moisture in 24-48 hours of high humidity. Without active drying, PETG prints develop popping sounds, stringing, and matte surfaces. The S2 dries a fresh spool in 4-6 hours and keeps it dry during long prints via the passthrough.
Nylon absorbs moisture from air in hours, not days. Print-while-drying via the passthrough is essentially mandatory for reliable nylon printing. The 70°C max is sufficient for nylon (typical drying profile is 70°C / 8 hours).
The S2 holds one spool. Multi-color users either buy multiple S2 units or step up to the SUNLU S4 (4 spools, $130). For 4-color cosplay or tabletop printing, the S4 is the better economy.
Better alternative: sunlu-s4-filament-dryer
The Bambu AMS has a desiccant compartment but no active heating — it maintains dry filament rather than drying wet filament. An S2 (or S4) for pre-AMS drying complements the AMS rather than replacing it.
Better alternative: Bambu Lab AMS
Dry desert climates rarely have moisture problems. PLA is the least hygroscopic common filament. Spend the $45 on filament instead — you'll get more printing value than from a dryer that runs once a year.
PEEK requires 120-150°C drying. The S2 maxes at 70°C, which is insufficient — wet PEEK still prints poorly even after 24 hours in the S2. PolyDryer or industrial filament dryers are the right choice for PEEK.
Ecosystem & Community
The S2 is the most-recommended hobby-grade filament dryer in the r/3Dprinting community (1.2M members). Printables hosts 100+ community-designed mounts and bowden adapters.
Compatible Software
What to Build First
Print a structural nylon bracket directly from a freshly-loaded S2 with the passthrough running at 70°C the entire print. The result is layer adhesion you cannot get any other way — the difference between a useful nylon part and a brittle prototype is whether the filament stayed dry during the multi-hour print.
View tutorial →Must-Have Accessories
Video Reviews & Tutorials
Tutorials & Resources
- SUNLU Filament Drying GuideMaterial-by-material drying temperature and time recommendationstutorial
- Best Filament Dryers RoundupComparison of S2, S4, eBox, PolyDryer, and other consumer filament dryersreview
- S2 Mods on PrintablesCustom mounts, larger spool adapters, and improved airflow mods for the S2project
Frequently Asked Questions
How long does it take to dry a wet spool?
Depends on material and starting moisture. Typical: PLA 4-6 hours at 50°C, PETG 4-6 hours at 65°C, ABS 4-6 hours at 70°C, nylon 8-12 hours at 70°C. Severely wet spools may need 1.5x these times. The audible popping during printing is the test — dry spools print silently.
Can I dry PEEK or ULTEM in the S2?
No. PEEK and ULTEM require 120-150°C drying temperatures. The S2 maxes at 70°C, which is insufficient — wet PEEK will still print poorly even after 24+ hours. For these materials, use the PolyDryer Box (130°C) or a dedicated industrial filament oven.
Does the S2 work as a long-term storage solution?
Yes — keep the S2 running at 40°C continuously to maintain dry filament between prints. Power draw at 40°C is roughly 15W, costing about $1.50/month. For nylon and PA-CF in humid climates, this is the most reliable filament storage method.
Is the print-while-drying passthrough reliable?
Yes for direct-drive printers and rigid filaments (PLA, PETG, ABS, nylon). Bowden printers with long filament paths plus very flexible TPU (85A, 90A) sometimes have feeding issues from the added friction. For TPU 95A and harder, the passthrough works reliably.
Will the S2 fit a 1kg eSun or Hatchbox spool?
Yes. The S2 fits any 1.75mm or 2.85mm spool up to 1kg / 200mm diameter, including eSun, Hatchbox, Polymaker, Overture, and Bambu spools. The chamber is brand-agnostic. Larger 2kg spools (250mm+) do not fit — those need the SUNLU S4 or a custom dry box.
Do I need a dryer for PLA?
Usually no. PLA is the least hygroscopic common filament and absorbs moisture slowly. In humid climates (Gulf Coast, Southeast Asia) or after 6+ months on a shelf, PLA can show mild moisture symptoms (slight stringing, occasional bubbles). For most PLA users in moderate climates, drying is unnecessary.
S2 vs S4 vs Bambu AMS?
Different roles. S2 dries one spool. S4 dries 4 spools. The Bambu AMS does not dry filament — it maintains dry filament with desiccant but lacks active heating. For multi-color drying, get the S4. For multi-color printing on a Bambu printer, get an AMS plus an S2/S4 for pre-AMS drying.