eSun eBox Pro 3D Printer Filament Dry Box Review

The Verdict on Filament Dryers

A filament dryer is easily one of my favorite 3D printing accessories. While this review focuses on the eSun eBox Pro, having a dedicated filament dryer in general is an absolute game-changer—especially if you want to print hygroscopic materials like TPU and PETG successfully.

When I first started printing PETG, I quickly realized that a simple drybox wasn't going to cut it. There is a common misconception that storing filament in an airtight box with a bunch of silica gel is a complete solution. While a drybox is great for preventing moisture absorption, it cannot effectively extract moisture once a spool is already saturated. For that, you need an active, heated dryer.

Another common misconception is what "wet filament" actually means. It doesn't mean the filament feels wet to the touch on the outside; the moisture is absorbed deep inside the plastic's polymer chains. The only way you usually find out it's wet is when you try to print and end up with excessive stringing, popping noises from the nozzle, and weak layer adhesion.

Reviewing the eSun eBox Pro

As for the eSun eBox Pro, a single slot filament, it largely delivers on its promises, though it comes with a few quirks you should know about.

Performance and Design

The eBox Pro functions brilliantly as an active dryer. You can dry the spool and feed it directly into your printer simultaneously.

Fast and Even Drying: The unit successfully reduces internal humidity from 60% down to approximately 35% within just 30 minutes of operation. It maintains a stable temperature without overheating.
Built-in Fan: Unlike older or cheaper models, the internal fan ensures uniform heat distribution. You don't have to worry about manually rotating the spool to get an even dry.
Direct Feeding: The lid features two PTFE tube outlets, allowing you to seamlessly feed the filament from the dryer directly into your extruder while the drying cycle is active.

The Quirks: Humidity Readings and Storage

While it works well as a dryer, it is not an airtight container. You will still need dedicated, sealed storage for long-term safekeeping. Because it isn't completely sealed, if you leave a spool sitting in the unheated unit for a couple of days, it will start to absorb ambient room moisture again. I tested this by leaving a spool inside for three days; when I printed with it, I noticed some minor stringing on the initial bridging. It was still a passable print, but noticeably less clean.

There is also a quirk with the Relative Humidity (RH) sensor that can be confusing at first. Even if you dry your filament for 8 hours at 65°C and achieve an RH of below 20%, the reading will spike once you turn the unit off and let it cool to room temperature. When you turn it back on at an ambient 35°C, it might read 60% RH.

This isn't necessarily a broken sensor—it is just the science of Relative Humidity. As the air cools, its capacity to hold moisture shrinks, making the relative percentage higher even if the filament itself hasn't absorbed new water.

Recommended Workflow

Because of how the eBox Pro operates, you don't need to run it constantly:

The Initial Bake: If a spool is wet, give it a full 8-hour drying cycle.
Printing: Even if the sensor reads 60% RH after the unit has cooled down, as long as it was fully dried recently, you can print immediately with great results and zero stringing.
Maintenance Drying: You don't need to leave the heater on for the entire duration of a long print. I usually turn it on for just 1 hour to warm things up, then turn it off while the printer finishes the job. As long as it underwent the initial deep dry, the filament will perform perfectly.

Final Thoughts

The eSun eBox Pro does exactly what it needs to do: it actively removes baked-in moisture and allows for direct-to-printer feeding. Just remember that you still need a separate airtight solution for long-term storage, and don't let the fluctuating RH sensor trick you into over-drying your filament.