SUNLU S4 Filament Dryer

SUNLU FilaDryer S4 Review: 4 Spools Filament Dryer

Better known as a filament manufacturer, SUNLU brings filament maintenance solutions to the market. The SUNLU FilaDryer S4 filament dryer is their latest product. Over the years, I’ve accumulated many half-empty spools of filament that have lost their quality due to humidity. Let’s see if I can refresh four spools at once. We’ll review the device, explore why we need it, and try out some of the setups.

Table of Contents

SUNLU FilaDryer S4 Specifications:

Large Filament Dryer
Size: 458mm x 218mm x 312mm
Fast Heating Up Speed
Intelligent Humidity Control
Number of Spools: Up to 4
Filament feed from the sides and top
Where to Buy?
Price: $129.99.
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SUNLU S4 3DWithUs Editor's Picks Award

Official Website

Previously, SUNLU launched two products via Kickstarter: filament dryer S2 and 3D printer SUNLU S9 Plus. For many companies, Kickstarter is a convenient pre-order platform. It is difficult to predict if a new product will meet demands, and it is commercially and environmentally important not to create more products than required. At the same time, to keep the price down, mass production is still the preferable manufacturing option.

Unboxing and Assembly

The FilaDryer S4 arrived assembled in a well-packed box, complete with a user guide leaflet, Teflon tubes, and a power cord.

SUNLU FilaDryer S4 and Accessories
SUNLU S4 Unboxed
©3DWithUs – Photo: Max Funkner

– Teflon Tubes. Two 2m (3.28 ft) long and four 100mm (3.93 in) long.

– Power Cord. As one of the first testers, I received the device with a Chinese power cord. An adapter was easy to buy from Amazon but I bet other orders will have power cords according to their country’s location.

– Design. Following the success of their previous SUNLU S2, the company maintained the design idea of the device. Slightly transparent black acrylic box with a wide screen and green lights. Similarly to its predecessor, SUNLU S4 stands out with its futuristic look.

SUNLU S4 Lids Open - Four Spools
SUNLU S4 Lids Open – Four Spools
©3DWithUs – Photo: Max Funkner

– Large Space. SUNLU works well with four 1kg filament rolls. It also works well with 750g spools. With smaller spools, I would use this machine for drying only, just in case the small spool gets on the side and gets stuck or creates extra tension during the print.

Inside Filament Dryer
Inside FilaDryer S4 – tape holds components in place during transportation
©3DWithUs – Photo: Max Funkner

– Three Fans. In the image above, you can see one side of the triple fan system. Also, apparently, in the middle, there is a compartment for the desiccant dehumidifier if needed (not included) to use the device as a filament storage box.

– Eighth Holes. Altogether, for the filament feed, there are 8 holes. Two from each side and 4 from the top.

SUNLU S4 Loose Lid Fix
SUNLU S4 Loose Lid Fix
©3DWithUs – Photo: Max Funkner

– Top Lid Quick Fix. One of the top covers was loose. Using a thin but sturdy object, I pushed the hinge nail into position. That was a quick fix.

– Storage. In order to use this device as a storage dry box when not operable, apart from adding desiccant dehumidifiers we need to use either plugs or stickers to cover them.

Working Mode

It took me approximately four hours to get the humidity (RH) from 45% to 26%. I bet this may vary depending on how wet my filaments are. I need more time to test my other spools. I will keep this post updated.

SUNLU S4 Screen - PLA Mode
SUNLU S4 Screen – PLA Mode
©3DWithUs – Photo: Max Funkner

What was a pleasant surprise is that the next morning humidity level went from 40% to 27% in 5 minutes.

– Noise. Fans are powerful indeed, but also noisy. I measured decibels (dB) with the lid open and closed. Here are the results. With the lid closed, the noise is comparable to a conversation at home.

SUNLU S4 Noise - Lid Closed-Open
Decibel Meter – Noise – Lid Closed-Open
©3DWithUs – Photo: Max Funkner

As often happens during Kickstarter campaigns, the R&D team is already working on improvements and has come up with a solution. The next batch, for backers and overseas warehouses after the crowdfunding, should come with this improvement implemented.

Setups with 3D Printers

Let’s put some 3D printers next to SUNLU S4 and see if the filament feed actually works. As this device is quite big, it takes some space depending on positioning. In my case, my table has enough space for both SUNLU S4 and the 3D printer.

SUNLU S4 Feeding Filament to AnkerMake M5
SUNLU S4 Feeding Filament to AnkerMake M5
©3DWithUs – Photo: Max Funkner

The filament feeding angle is just right for 3D printers such as Ender 3 V2 Neo or AnkerMake M5. In fact, at such an angle, the filament gets fed more safely than from the filament holder installed at the top. Such an angle would be safer for brittle filaments, such as wood filaments, for example.

SUNLU S4 and Original Prusa
SUNLU S4 Feeding Filament to Original Prusa i3 MK2.5S
©3DWithUs – Photo: Max Funkner

I was pleased to see that FilaDryer S4 worked well with my 7-year-old upgraded Prusa i3 MK2.5S. Not sure if there will be obstacles if the print will get higher, though. I would position the dryer slightly higher when printing with exotic brittle filaments, just in case.

Importance of the Teflon Tubes

SUNLU S4 struggles to feed 3D printers with filament sensors positioned at the top or too high. From the dryer, the filament performs a sharp curve before getting into the extruder. Brittle filaments, like wood filament, for example, will just snap in such situations. But such an angle is too sharp for PLA as well.

SUNLU FilaDryer S4 and FDM 3D Printers
FilaDryer S4 is equipped with Teflon for the smooth filament feed.
Photo: SUNLU

Here is what may happen if Teflon tubes are left unequipped. The tension created is too high.

FilaDryer S4 Feeding Filament to Neptune 4 Pro
Filament Travel Curve is Too Sharp
First Layer Fail
Failed First Layer – Result of the Excessive Tension
©3DWithUs – Photo: Max Funkner

As a result of excessive tension, in my case, even the first layer showed the difference. When there was plenty of filament, Elegoo Neptune 4 Pro performed a perfect first layer, but then tension kept the extruder slightly higher. Miraculously, there are no signs of under-extrusion but a sign of a too-high Z offset.

SUNLU S4, SUNLU S2 and Elegoo Neptune 4 Pro
SUNLU S2 position is just about right
©3DWithUs – Photo: Max Funkner

As instructions suggest, the Teflon tubes should be installed, especially if there is a sharp filament travel curve.

Why We Need It and Other Filament Dryers

I keep all my filament in sealed plastic bags with a piece of desiccant dehumidifier and am generally happy about it. Of course, over a few years’ time, the quality of filament in some of the spools has degraded due to general mishandling. Plastic bags either weren’t sealed properly, were micro-pierced by a sharp filament end, or the silica gel just stopped working and I had no idea about it. In the end, humidity affected the quality of the filament to some degree.

In extreme cases, during extrusion, my filament made a popping noise and some visible evaporation happened. This is the source of uneven surfaces on the prints. When the water is heated, it boils and evaporates leaving micro craters on the extruded filament and printed surfaces.

SUNLU S4 and SUNLU S2 Filament Dryers
SUNLU S4 and SUNLU S2 Filament Dryers
©3DWithUs – Photo: Max Funkner

Earlier, we wrote a comprehensive guide about filament dryers, discussing why we need them and delving into moisture absorption – hygroscopicity. We also compared the best filament dryers and DIY solutions available on the market.

Conclusion and Pros & Cons


Official Website

SUNLU FilaDryer S4 Review

Review Summary

I am really pleased to have SUNLU FilaDryer S4 along with my FDM 3D Printers. Over the years, I’ve accumulated a lot of half-empty spools that have lost their quality due to humidity. Now I can refresh them four spools at once. It is definitely a good device for FDM 3D printer workshops. Also, it can be a fancy alternative to a filament storage box for casual 3D printer users as well.



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