Damp filament prints badly, so I bought a filament dryer and started drying spools before printing. Trouble is, my Creality K2 Pro feeds filament through a unit called the CFS (Creality Filament System).

So the spool gets dried, and then it sits in the CFS at the mercy of whatever the humidity in there happens to be. Which rather defeats the point — so I bought the KING “OZO” strong desiccant, ultra-fast type (OZO-Z10). Here is how that went.

  • Humidity inside the CFS dropped from 65% to 39%
  • It climbed when I opened the lid to swap filament, then fell again once it was closed
  • Only three days in, though. Whether it lasts is still to be seen

Dropped the OZO-Z10 in, and 65% became 39%

29 August 2026, OZO goes into the CFS.

The CFS with its lid open — OZO sachets sit in the recess at the back right

Until then I had been running the silica gel that came with the CFS, and the unit’s own humidity readout sat at around 65%. Prints take hours, so I had a nagging feeling that drying a spool beforehand was not going to survive the print itself.

With the OZO in and the lid closed, the readout kept falling, and settled at 39%. Filament is generally said to keep best somewhere around 20–50% for PLA, so it is at least inside that range. It barely moved during printing, either.

The CFS readout shows 32°C and 39% RH; a hygrometer standing in front of it reads 31.2°C and 63%

The white unit at the front of that photo is a hygrometer sitting out in the room: 31.2°C and 63%. The CFS standing right next to it reads 39%. A 24-point gap.

A note on the link below: this is a Japanese product and I could not find it on amazon.com, so it points to amazon.co.jp. The listing is in Japanese, and whether it ships to your country is worth checking before you get your hopes up.

KING OZO Strong Desiccant, Ultra-Fast Type (OZO-Z10)

KING OZO Strong Desiccant, Ultra-Fast Type (OZO-Z10)

View on Amazon.co.jp

Filament swaps spike the humidity — but it comes back down

The part that impressed me most is actually this one.

Swapping filament means opening the CFS lid, so the readout jumps straight up. Nothing to be done about that. What is interesting is what follows: close the lid, come back a while later, and it has worked its way back down. The “ultra-fast” on the label is not just marketing.

The manufacturer claims roughly 7× the absorption of a silica gel type, with humidity falling in about three hours.

The humidity does go up every time I swap, but having it pulled back down this quickly is genuinely welcome.

What I can’t tell you yet

Being straight about it: I am writing this on day three of using it. All I have confirmed is that it works well right after you put it in.

The manufacturer states a lifespan of about 4–8 months. Whether that holds up with a lid that gets opened this often, I don’t know yet. For now I will keep an eye on the readout and swap them out when it starts creeping up.

Who this is for

  • You own a filament dryer but worry about humidity while the print is running
  • You leave filament loaded in a sealed unit like the CFS
  • You are running the bundled silica gel and it is not bringing the humidity down as much as you hoped

The sticking point is the price — it is not cheap. Whether it works out on cost depends on how long it lasts, which is what I will be watching.

The OZO ultra-fast type package lying on the floor next to a filament spool for scale

For what it is worth, I have only tried this in a Creality K2 Pro’s CFS. Whether other vendors’ equivalent units see the same effect, I have not checked.

Wrapping up

Humidity in the CFS went from 65% to 39%, and it recovers after I open and close the lid. With the room itself at 63%, that gap is doing real work. Three days in, I am simply glad I bought it. If I learn how long it lasts, that is probably its own post.

KING OZO Strong Desiccant, Ultra-Fast Type (OZO-Z10)

KING OZO Strong Desiccant, Ultra-Fast Type (OZO-Z10)

View on Amazon.co.jp