SUNLU Filament Dryer S4 - 4-Spool Filament Dry Box for 3D Printing

In this review the SUNLU Filament Dryer S4 is evaluated as a practical solution for makers and small print farms who need reliable, multi-spool filament storage and drying. The S4's strongest selling point is its capacity to handle four 1kg spools while automatically controlling humidity and temperature, making it a single unit that replaces multiple dryer setups and reduces print failures from damp filament. For anyone running multiple machines or switching colors frequently, the S4 simplifies storage and keeps filament print-ready.

Key Features

• Large 4-spool capacity: Holds four 1kg spools at once so users can run multiple printers or store a variety of materials without repacking or rotating spools.
• Fast 350W PTC heating: The high-power heater brings the interior up from room temperature to drying range in roughly 30 minutes, cutting prep time before long prints.
• Auto humidity control: User-selectable humidity modes let the dryer start when humidity rises into the chosen range and stop when the filament is dry, reducing over-drying risk.
• Triple-fan balance: Two side circulation fans and a bottom fan keep internal temperature within about 3C for uniform drying across all spools.
• Triple safety protection: Built-in PTC, a temperature switch and software safeguards provide monitoring and alerts to prevent overheating and keep storage safe.

Who It's For

The S4 is best for hobbyists with several printers, prosumers running occasional small production runs, and educators managing a lab where several filaments need to stay dry and ready. Its 4-spool capacity and multi-printer compatibility suit users who change colors or materials often and want a single, consolidated drying solution.

Less appropriate are users who only ever print with a single spool and have extremely tight bench space, since the S4 is designed around multi-spool convenience rather than minimal footprint. Also, those needing active filament drying at very high temperatures for specialty materials should verify compatibility before purchase.

Pros & Cons

Pros

• Large internal space supports four full 1kg spools for uninterrupted multi-color or multi-machine printing.
• Quick, efficient heating from the 350W PTC element shortens preprint preparation time.
• Smart humidity control with auto start/stop reduces manual monitoring and prevents over-drying.
• Balanced airflow from three fans ensures even drying across the whole box.

Cons

• Because it is sized for four spools, the unit is larger than single-spool options and may not suit very small workspaces.
• Specialty filaments with unusual high-temperature requirements may need separate dedicated drying solutions.

Specifications

Brand	SUNLU
Model	Filament Dryer S4
Spool capacity	4 spools (1kg each)
Heater	350W PTC heater
Humidity control	Auto humidity mode (approx. 30%~50% adjustable, stops below 25%)
Air circulation	3 fans (2 side, 1 bottom) for temperature balance within ~3C
Safety features	PTC, temperature switch, software protection

Our Verdict

The SUNLU Filament Dryer S4 is a strong value for makers and small shops that need a reliable, multi-spool drying and storage solution. Its 4-spool capacity, fast 350W heating, and smart humidity control cut down print downtime and filament waste, while triple safety features add confidence for unattended drying. For anyone running multiple printers or regularly swapping materials, the S4 simplifies filament management and is worth the space it requires.

Frequently Asked Questions

Can the S4 run multiple printers at once?
The S4 supports connections to multiple printers and can feed up to four printers or hold four spools for simultaneous use.

How long does it take to reach drying temperature?
With the 350W PTC heater the box reaches roughly 50C from 25C in about 30 minutes under normal conditions.

Will it prevent over-drying?
Yes; the smart auto humidity control stops active drying when internal humidity falls below about 25% to avoid excessive drying.