SUNLU S4 vs Space Pi Plus: 4 Spools or 2?

Choose the SUNLU S4 for recurring four-spool work

The S4 earns its larger footprint when the bottleneck is serial drying. Its official page lists internal dimensions of 450 × 210 × 211 mm, capacity for four 1 kg spools, a 70 C ceiling, two side circulation fans plus a bottom heating fan, and simultaneous feeding for as many as four printers. That combination is useful for multicolor projects, a bench with several active materials, or a small print farm that repeatedly stages multiple spools under one compatible program.

The phrase compatible program matters. Four positions do not create four temperature zones. If PETG, TPU, nylon, and support material all need different maker-specified time and temperature treatment, filling every position may not save a cycle. The S4 is strongest when multiple spools can safely share one chamber setting and finish together.

Do not buy it merely because four is larger than two. A box that runs half empty most weeks consumes more bench space without solving a new problem. Read the full SUNLU S4 review if the exact four-spool product is the remaining decision.

See the validated SUNLU S4 listing.

Choose the Space Pi Plus for the cleaner two-spool default

The original Space Pi Plus is the better default for a home or studio bench that normally has one loaded spool and one next-up spool. The exact original retailer listing describes two-roll capacity, double PTC heating, 360-degree hot-air circulation, a 45-70 C range, a 0-48 hour timer, a 3.7-inch touchscreen, two filament ports, PTFE tubes, and support for 1.75 and 2.85 mm filament. Creality's current U.S. direct-store route now serves V2 Plus, so verify the generation instead of assuming that every Space Pi Plus page describes the original unit.

That is enough capacity for many PETG-and-TPU benches without turning the dryer into the largest accessory near the printer. For a PETG-heavy bench, use the PETG dryer-versus-storage decision before assuming every open spool needs another heat cycle. The two-feed-path layout is easier to plan when two positions are sufficient; the tradeoff is that a third damp spool starts a second batch, while the S4 may clear all four in one compatible cycle.

The Space Pi Plus is not automatically weaker because it holds fewer spools. If two positions cover almost every real job, the smaller capacity is the more efficient match. The full Space Pi Plus review owns the exact-product fit.

See the validated Creality Space Pi Plus listing.

Run this five-question workload test before buying either

1. How many damp or moisture-sensitive spools appear in a normal seven-day period? Count real spools, not future colors that might never be opened.
2. Can they share one drying program? Capacity only helps when the filament maker's temperature and time guidance overlap.
3. Will the dryer feed a printer? Map filament exits, PTFE bend radius, lid clearance, cable reach, and the path into the extruder before measuring only the box.
4. Is the job recovery or maintenance? A visibly wet spool may need a full recovery cycle. An already dry spool may only need controlled feeding and storage between jobs.
5. Where does the spool go afterward? Returning a dried spool to an open shelf recreates the moisture problem. A dryer and sealed storage do different jobs.

Choose the S4 when the answers repeatedly point to three or four same-program spools. Choose the Space Pi Plus when one or two positions clear the real queue. Choose a different route when temperature headroom, unusually large spools, or independently controlled chambers matter more than raw position count.

Neither dryer makes one universal material preset safe

PLA, PETG, TPU, ABS, ASA, nylon, polycarbonate, filled blends, and support materials do not share one universal drying recipe. Brand, formulation, spool construction, starting moisture, and the filament maker's guidance matter. A device menu is a convenience, not permission to ignore the spool manufacturer's limit.

For ordinary PETG and TPU rotation, both dryers offer enough listed temperature range to be credible workflow tools when the exact filament guidance fits. For demanding nylon or polycarbonate recovery, verify the required temperature and duration before assuming a 70 C ceiling is enough. If the material guidance needs more temperature or the spool is unusually large, the EIBOS Polyphemus review explains a different larger-spool, higher-temperature lane.

If the print symptom is still ambiguous, start with how to tell whether filament is actually wet. Stringing, rough surfaces, weak extrusion, and popping can have other causes; for PETG specifically, work through the PETG stringing checklist before treating every strand as moisture. A dryer should fix a diagnosed moisture workflow, not replace basic printer troubleshooting.

Drying, dry feeding, and sealed storage are three different jobs

Active drying uses heat and airflow to remove moisture. Dry feeding reduces exposure while a spool is printing. Sealed storage slows moisture uptake after the active cycle. The S4 and Space Pi Plus can cover the first two jobs, but neither makes an open shelf into controlled storage.

This distinction changes the value decision. Four damp spools arriving together favor the S4. Two spools that print throughout the week favor the Space Pi Plus. Spools that are already dry but degrade between monthly jobs favor better storage first. The dryer, dry-box, or sealed-storage guide separates those purchases.

Check the physical system, not only the dryer

Before ordering, trace the complete feed path. Confirm the live spool diameter and width limits, the direction each spool unwinds, outlet position, PTFE length, bend radius, extruder entry angle, lid clearance, wall clearance, power-cord route, and access to the screen. A theoretically compatible dryer can still be awkward if the tube must cross the enclosure door or turn sharply into a side-mounted extruder.

Keep the machine on a stable, heat-tolerant surface with its ventilation unobstructed. Use the current manual and local electrical requirements. Do not treat either appliance as an unattended cure-all, and do not put a spool into a temperature cycle that exceeds the filament or spool maker's guidance.

Do not use wattage as the tie-breaker

SUNLU's current base-S4 page contains conflicting power language: its marketing copy describes a 350 W PTC heater, while a specifications block shows 300 W rated power. The exact original Space Pi Plus retailer listing describes 110 W PTC heating, while Creality's current U.S. route now serves V2 Plus and other Space Pi variants can show different figures.

Those conflicts are a reason to verify the current listing and manual, not a reason to invent a precise energy-cost winner. More input power also does not automatically mean a spool dries better; chamber volume, airflow, venting, starting moisture, load, ambient conditions, and cycle duration all affect the result. Buy on measured workload and accepted output, then verify live electrical specifications before checkout.

How to prove the purchase after it arrives

1. Use one known filament, one representative spool, and the filament maker's safe drying guidance.
2. Record the starting symptom: popping, inconsistent extrusion, surface roughness, or another repeatable sign.
3. Run a controlled cycle without mixing materials that need different programs.
4. Print the same small test with the same printer, profile, model, and environment.
5. Judge the accepted result, not merely the chamber display or humidity number.
6. Move the spool into its real feed and storage workflow, then check whether the improvement survives several days.

If the output does not improve, recheck whether moisture was the cause, whether the cycle matched the exact material, whether the spool could rotate and vent correctly, and whether the feed path reintroduced friction or exposure. That proof is more useful than assuming the larger machine must be better.

Final verdict

Buy the original SUNLU S4 only if three or four compatible spools repeatedly share one program and its exact delivered price stays meaningfully below S4 Pro. In the Oct. 5 official U.S. snapshot, the gap was only $23.00.

Buy the original Creality Space Pi Plus if one or two active spools describe the workload and an exact original-model listing has acceptable seller, plug, warranty and return terms. Do not mistake the current U.S. V2 Plus page for the original product compared here.

Buy S4 Pro instead when two independently controlled zones, its listed 85 C ceiling, or its drying-and-annealing workflow removes a measured constraint. Buy neither yet if moisture has not been diagnosed or controlled storage is the real missing step.

Check SUNLU S4 availability or check Creality Space Pi Plus availability.

Frequently asked questions

Is the SUNLU S4 hotter than the Space Pi Plus?

No meaningful listed-temperature advantage separates them: both currently show a 70 C ceiling. The S4's advantage is four-spool capacity; the Space Pi Plus's advantage is a smaller two-spool workflow.

Can both print directly from the dryer?

Both are positioned for feed-through use. The S4 official page describes feeding up to four printers, while the current Space Pi Plus listing describes two ports and PTFE tubes. Verify the full physical route to your printer before buying.

Is the S4 automatically better for a Bambu AMS?

No. A generic external dryer does not automatically become an AMS-integrated system. Plan the transfer, spool fit, PTFE routing, and exposure between drying and loading rather than assuming capacity alone solves AMS humidity.

Can I dry PETG and TPU together?

Only when the exact filament makers' safe time and temperature guidance overlaps. Material-family names are not a universal shared preset.

Does either dryer replace vacuum bags or dry boxes?

No. Active drying removes moisture; sealed storage slows moisture uptake after the cycle. A reliable workflow often uses both.

Which is better for one printer?

The Space Pi Plus is usually the cleaner one-printer default when one or two active spools are normal. The S4 still makes sense if that single printer uses multicolor or several moisture-sensitive spools often enough to create a recurring batch.

Source check: SUNLU S4 specifications, exact base S4 U.S. offer, S4 Pro U.S. offer, Creality U.S. V2 Plus route, and both exact original-product retailer listings were checked October 5, 2026. Confirm live generation, price, stock, plug, seller, warranty and returns before ordering.