SUNLU S4 Pro Filament Dryer

Drying and annealing range

SUNLU sells the S4 Pro as a dual-zone dryer with independent temperature and time control per zone, so PLA or PETG can dry in one chamber while PA, PC or PP is conditioned in the other. Each zone measures 220 × 210 × 211 mm internally, which takes a 1 kg spool comfortably but not a 2 kg spool as standard; the 4 × 1 kg figure is a capacity claim, not a 2 kg claim. The maximum is 85 °C / 185 °F, and SUNLU confines the built-in annealing mode to materials and printed parts with an annealing temperature of 85 °C or less. 3DPrint.com, which covered SUNLU’s E2 in February 2025, puts PETG annealing at roughly 90–110 °C and warns that overheating deforms parts. If your material is PA, PC, PP or fibre-reinforced variants you are inside the Pro’s range; if you want to anneal PETG you are not.

Evidence: measured versus unmeasured

No independent instrumented test of the exact S4 Pro exists. Searching the exact product name returned only SUNLU’s own store and general SUNLU pages, with no reviewer, retailer or forum page indexed; no RTINGS, Wirecutter, Tom’s Guide, CNET or PCMag test surfaced, and no owner thread. Nothing was published for the S4 Pro on zone-to-zone temperature difference, chamber humidity accuracy, warm-up time, sound level, energy use or drying results on any material. The absence of a published accuracy figure stands out because SUNLU publishes one for its E2: ±3 °C at 70 °C in a 25 °C environment and ±5 °C from 70 °C to 110 °C, measured at four points. Those E2 figures describe a different machine and are not evidence about the S4 Pro.

Running costs, parts and upkeep

The recurring costs are filament, electricity and feed-through tubing. The S4 Pro is rated at 380 W, but SUNLU publishes no duty cycle, measured draw or energy-use figure, so running cost can only be estimated from a duty cycle you define. The box ships two 1 m PTFE tubes, against two 100 cm and four 8 cm tubes for the older S4, which marks the feed-through tubing as a periodic replacement item. The accessory kit carries eight stainless steel shafts and sixteen bearings, which points to a two-bearing-per-spool mount and suggests the spool holders are user-serviceable, a plus for long-term ownership. No spare-parts catalogue or service manual for the S4 Pro was found, and the printed manual has no located digital version.

Warranty and where you can buy

SUNLU’s store-wide after-sales policy gives direct buyers 14 days for refund and return in new, unused condition with all parts and tags included, a 30-day exchange window, and warranty as the only recourse after those windows. Eight categories of damage are excluded, including misuse, third-party repair, non-quality issues after 30 days and purchases without proof of purchase. Return shipping is paid by the buyer; SUNLU covers shipping or quality damage after a support email. The policy states it applies only to products bought from the SUNLU Official Website, and tells buyers on eBay, Amazon, AliExpress and authorised resellers to deal with those sellers directly. The adjacent S4 is published at one year with exclusions for non-original power supplies; use one year for the S4 Pro only as a working assumption until its warranty text is read.

Is it worth it?

$139.99 is defensible but narrow. The S4 Pro sits about $23 above the single-zone S4 at $116.99 and roughly $110 below the E2 at $249.99, and the trade press has called SUNLU’s dryer pricing expensive next to the Creality Plus Space Pi at $100, the EIBOS at $140 and the PrintDry four-spool at $199. The case for the premium rests entirely on the second independently controlled zone; a shop that prints one material type has no use for it and can take the S4 and keep the $23. The thresholds: at or below $120 it is strong, $121–140 defensible, $141–160 weak to fair, and above $160 poor. The EU-plug variant already sits at $149.99, where the E2 becomes worth costing out for its 25 °C of extra headroom, published accuracy and UL, CE, FCC, UKCA and ROHS certification.

Which model this is

This page covers the SUNLU FilaDryer S4 Pro, model S4Pro, sold only in Black with US, EU and AU plug SKUs. The US-plug SKU is shared by the Ship to USA and Ship to Canada variants, and the AU-plug variant is listed at the same price but out of stock. Do not merge it with the single-zone FilaDryer S4 (model S4-FD, 320 W), the 110 °C E2, the SP2 or the S1/S2 dry boxes. The Amazon listing for this model is ASIN B0H6X1JXPG.

Sources

Manufacturer:

• SUNLU FilaDryer S4 Pro product data (SUNLU Official Store)
• SUNLU filament dryer collection (SUNLU Official Store)
• SUNLU refund and after-sales policy

Independent reviews:

Owner reports:

• No owner reports for the S4 Pro were located in this run.

Parts and stores:

• SUNLU wiki entry for the FilaDryer S4 Pro