SUNLU S4 vs S2: premium 4-spool drying or budget drying done right?

Display / screen quality

The S4 wins here on paper, mainly because it’s the newer flagship-style unit with auto humidity control and a more modern user experience. Even without a full spec sheet in front of us, the S4’s positioning as the 2026 newest model strongly suggests a more polished interface for monitoring drying status and humidity. The S2 is functional and gets the job done, but it’s the older, simpler option aimed at straightforward drying rather than premium control. Winner: S4, because it is the more advanced and user-friendly product.

Performance

This is the biggest category, and the S4 takes it. The S4 is described as an upgraded 4-spool filament dehydrator with fast heating and temperature balance, which means it’s designed to dry multiple reels at once while keeping conditions more even across the chamber. That matters if you run a busy printer farm, switch between materials often, or keep several reels ready to go. The S2 is no slouch: it offers 360° all-round heating, a 70°C max temperature, and a fan, which is excellent for drying a single spool efficiently. But it cannot match the S4’s multi-spool capacity or its smarter control approach. Winner: S4 for throughput and convenience; S2 only wins if you just need one reel dried at a time.

Build quality and design

The S4 looks like the more refined product. Its “filaments storage box” positioning implies a more integrated design for keeping multiple reels dry and ready, and the emphasis on temperature balance and auto humidity control suggests a more premium internal layout. The S2 is a classic dryer box design: practical, compact, and well understood by the community. It’s likely easier to live with on a small desk or next to a single printer because it has a simpler footprint and fewer bells and whistles. If you want a more robust all-in-one storage-and-drying solution, the S4 wins. If you want a no-nonsense box that does one job well, the S2 is perfectly respectable. Winner: S4 overall, with S2 earning points for simplicity.

Battery life

Neither product is battery-powered, so this category doesn’t really apply in the usual sense. What matters instead is continuous mains-powered operation and stable long-duration drying. On that front, both are built for plug-in use, but the S4’s auto humidity control and temperature balance should make it better suited to leaving spools in the box for longer without babysitting. The S2 is still capable for extended drying sessions, especially for moisture-prone materials like PETG, ABS, PA, and PC, but it is less sophisticated. Winner: S4, by virtue of better long-duration control.

Price and value for money

This is where the S2 fights back hard. At £44.99, it costs £55 less than the S4, which is a huge saving in filament-dryer terms. For many hobbyists, that difference could buy several rolls of PLA or a decent nozzle upgrade set. The S2 also has a solid 4.4/5 rating from 643 reviews, which suggests it’s a trusted, good-value choice. The S4’s 4.7/5 rating from 1,070 reviews is stronger, and the extra confidence from more reviews matters. But value isn’t just about being cheaper; it’s about what you actually need. If you only dry one spool at a time, the S2 is outstanding value. If you need four-spool capacity and smarter control, the S4 justifies its premium. Winner: S2 for pure value, S4 for value at the high end.

Game library / features

Translating this category into filament-dryer terms, the S4 is the clear feature winner. Its headline advantages are upgraded 4-spool support, auto humidity control, fast heating, and temperature balance. That’s a proper feature set for makers who want less fiddling and more consistency. The S2 still has meaningful features: fan-assisted 360° all-round heating and a 70°C max temperature, which is enough for a wide material range including PLA, PETG, TPU, ABS, PA, and PC. But compared with the S4, it’s the simpler machine. Winner: S4, because it offers more automation and capacity.

Overall user experience

The S4 is the better experience if you value convenience, capacity, and set-and-forget drying. It’s the one to buy if your printing habits are serious enough that you want multiple spools dry and ready, or if you hate manually managing humidity. The S2 is easier to recommend for most everyday makers because it’s cheaper, proven, and still capable across a broad range of filaments. In practice, the S2 will satisfy a lot of users who just want better prints from damp filament without spending a fortune. But the S4 feels like the more complete product and the better long-term buy for heavier users. Winner: S4 overall.

Overall summary: the SUNLU S4 is the better dryer, but the SUNLU S2 is the better bargain. If you want the most capable, feature-rich, multi-spool solution, buy the S4. If you want reliable drying for one or two reels without blowing your budget, the S2 is the smarter purchase.