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Filament Dryer - Sunlu S4 review.

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Filament Dryer - Sunlu S4 review.
My Sunlu S4 filament dryer

Living in a high-humidity region of the UK, I’ve battled brittle, popping, and tangled filament for years. Enter the Sunlu S4 filament dryer—a Kickstarter-backed gadget that promises to dry up to four 1kg spools at once (or 3 kg with a 3D-printed adapter). Does it actually rescue damp filament? Here's how it performed in real-world use.

What’s in the Box

  • Sunlu S4 filament dryer unit
  • Power cord and control panel
  • Space for four 1 kg spools, plus optional adapter for larger spools (useful for filament rolls up to 3 kg)
  • Quiet heating system that claims to reduce humidity below 25% in hours

Real-Life Drying Tests

1. Reviving a Year-Old Red Filament

This filament had been on the spool for over a year - virtually guaranteed to trap moisture. After a 4-hour drying cycle (aiming for 25% humidity), I loaded it into my updated hot end (Phaetus). The result? Smooth, squeak- and crack-free prints - no popping at all.

2. Breathing Life into a Gray Filament

Stored in a dry box, this spool fared better - but still held its breath when taken fresh from storage. After drying in the S4, it performed flawlessly on both my CR-10 Max and for my first Benchy test print.

Handy for Multi-Printer Setups

With two printers in my setup, the S4’s four-roll capacity was a game-changer. It fed both machines simultaneously, while letting me pre-load up to two more rolls for the next print batch. If you have an AMS system, this is also great for that as well.

What Could Be Improved?

As a Home Assistant user, I'd love to see Wi-Fi or MQTT-support baked in - for remote monitoring, managing dry cycles, or automating control. For now, I use a smart plug to control power, but a built-in automation interface would be next-level. In addition, the smart plug can't actually start the dryer on a cycle.

Final Verdict

The Sunlu S4 excels at its core function - drying filament reliably and quietly. It’s especially handy for multi-printer users or those with hobby automation setups. While automation features are absent, this unit is otherwise well-designed, functional, and worthy of a spot in your maker toolkit.

Here are some related items that pair well with the S4 - and yes, these are affiliate links to support the blog (at no extra cost to you):

About the author

Tim Wilkes is a UK-based security architect with over 15 years of experience in electronics, Linux, and Unix systems administration. Since 2021, he's been designing secure systems for a telecom company while indulging his passions for programming, automation, and 3D printing. Tim shares his projects, tinkering adventures, and tech insights here - partly as a personal log, and partly in the hopes that others will find them useful.

Want to connect or follow along?

LinkedIn: [phpsytems]
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