SUNLU filament dryers: S2 vs. S4 vs. SP2

Compare the three designs

These are published features, not comparative performance results. Maximum temperature does not show how evenly a loaded chamber heats or how long your particular spool requires.

Compare the package, not the starting price

The checked US listings showed S2 Black, one set, US plug: $44.99 and S4 Black, US plug, no filament bundle: $116.99. SUNLU also offers multipacks and packages with randomly selected filament; their headline prices are not directly comparable.

Price check: October 9, 2026. Listed US-dollar prices refer to the exact variants named, before tax and shipping. Promotions, colors, packages, and availability can change; confirm the final cart.

The SP2 listing had an unavailable USA variant and inconsistent package wording during our check. We therefore omit a current SP2 price. Verify that an offer includes the heater base if you need active drying, rather than purchasing a storage component alone.

If a bundle includes three rolls you would not otherwise buy, do not count their advertised value as cash saved. Compare the hardware-only cost with the cost of materials already on your shopping list.

Use your actual drying queue to choose capacity

Imagine you own eight colors but print one spool at a time. If only tomorrow's roll needs preparation, the S2 can still be the appropriate size. Owning eight colors does not create a requirement to heat eight positions.

At the checked single-unit prices, two S2 units total $89.98; one S4 is $27.01 more and provides up to four positions in one unit. This is a hardware-price comparison, not a claim about equal energy use, throughput, or drying performance. Two separate devices may also let you schedule different supported procedures independently.

For an S4, plan batches whose filament and spool instructions agree. Do not put mixed materials into a shared chamber and choose a compromise temperature that meets neither procedure. A material requiring a higher supported drying temperature may rule out all three models regardless of capacity.

Measure the desk and the reel

SUNLU lists S2 external dimensions of 265 × 274 × 118 mm; the S4 is listed at 458 × 218 × 312 mm. Check the manufacturer's dimension order and measure the real orientation you plan to use. Leave access for the lid, power connection, ventilation, and filament outlet.

The SP2 specification lists a large-spool limit of 250 mm diameter and 153 mm width. “Three kilograms” alone cannot establish fit: another manufacturer's reel can have different dimensions at the same net material weight.

Trace the complete feed route before deciding where a dryer will sit. Tubing should follow the supported arrangement without catching a moving bed or forcing a tight turn. If you intend to print from the device, read that model's operating instructions rather than treating every outlet as approval for every feeder.

Match equipment to the filament instructions

Start with the exact filament, then verify its recommended drying equipment, temperature, duration, and spool limits. Prusa’s guidance separates the material from the heat limits of the reel. A setting that a dryer can reach may still be wrong for the loaded spool.

A humidity display measures chamber air; it does not directly measure water inside the polymer. Do not end a procedure solely because the number fell after heating. Follow the supported cycle and evaluate a repeat print with the same settings.

For unclear symptoms, use our wet-filament diagnostic guide before buying hardware. Stringing or under-extrusion can have other causes. This comparison deliberately avoids universal drying temperatures and improvised household-oven methods.

Who should buy each, and who should wait

• Choose an S2 candidate for a modest one-spool workflow when its supported procedure and fit match your materials.
• Choose an S4 candidate when simultaneous capacity will save real preparation time and you have room for the loaded unit.
• Investigate SP2 when detachable chambers would reduce handling; wait until the exact complete package and needed spare chambers are confirmed.
• Wait on a dryer purchase if your existing filament prints well and the actual need is better storage between jobs.

Our dryer versus dry-box guide explains that distinction. For long-term ownership, add storage, desiccant, electricity, and maintenance to the price comparison. We have not verified noise, temperature accuracy, seal performance, or speed advantages, so none is used to rank these models.