Why Your Bambu AMS Needs Silica Gel (We Went from D to A)

Dry and Dry orange indicating silica gel beads in a 1-quart jug

When we set up our Bambu Lab P1S Combo, we figured the AMS would keep our filament dry on its own. It didn't. Even with the desiccant packets Bambu includes, our AMS humidity reading sat at a "D," which is near the bottom of the scale.

Adding rechargeable silica gel, plus a few 3D-printed boxes to hold it, got us all the way to an "A," the best reading. Here's what we learned about desiccants, why we went with silica, and exactly what we use.

Why the AMS Needs Help Staying Dry

The AMS keeps your spools in a closed box, but the original AMS doesn't heat or dry filament. It depends entirely on desiccant to soak up moisture.

That matters because filament absorbs water from the air. PLA is fairly forgiving, while PETG, TPU and nylon are much more sensitive. When damp filament hits the hot nozzle, the water turns to steam. You get popping sounds, stringing, rough or bubbly surfaces, weak layers and, sometimes, brittle filament that snaps inside the AMS.

And humid air gets in more often than you'd think. Every time you open the lid to swap a spool, a fresh batch of room air comes in with it.

The AMS has a humidity sensor that shows up in the Bambu Handy app and Bambu Studio as a letter from A to E. A is the driest, E is the dampest. If yours is sitting at C or worse, your desiccant isn't keeping up.

Desiccant vs Silica Gel: What's the Difference?

This one confused us at first. "Desiccant" is the general word for anything that pulls moisture out of the air. Silica gel is one type of desiccant. So all silica gel is a desiccant, but not every desiccant is silica gel.

Here are the common types you'll run into when shopping for filament storage:

Type	Good at	Drawbacks
Silica gel	Holds a lot of moisture for its size, safe and non-toxic, and recharges at low heat. Comes in indicating versions that change color.	Doesn't pull humidity quite as low as molecular sieve.
Molecular sieve	Grabs moisture fast and pulls humidity very low, even when the air is already fairly dry.	Needs much higher heat to recharge, so it's not microwave friendly. Usually not color indicating.
Activated alumina	Hard, durable beads that hold up to lots of recharging.	Also needs higher heat than silica to recharge.
Clay (bentonite)	Cheap and natural.	Holds less moisture and doesn't work as well when it's warm.
Calcium chloride	Absorbs a huge amount of water (it's what's in many closet moisture absorbers).	Turns into a salty liquid as it works, which can spill and corrode things. Not something you want near a printer.

For an AMS, silica gel and molecular sieve are the two popular choices. Molecular sieve can get humidity lower, but recharging it takes a lot more heat than a quick trip through the microwave.

Why We Chose Rechargeable Silica Gel

We went with silica gel, and specifically with silica we can recharge in the microwave. Here's why:

It's reusable. The packets that come with the AMS aren't rechargeable, so once they're full, they're done. Rechargeable silica can be dried out and reused over and over.
Recharging is quick and easy. A few minutes in the microwave and it's ready to go again. No need to tie up the oven for hours.
You can see when it's full. Indicating silica changes color as it absorbs moisture, so there's no guessing.
It's safe. Silica gel is inert and non-toxic, and the orange indicating kind we use is free of cobalt chloride.
It works well at room temperature, which is exactly where the AMS lives.

Orange vs blue indicating silica

Indicating silica comes in a few colors. The older blue kind uses cobalt chloride to change color, and cobalt chloride is toxic and has been restricted in Europe. Orange indicating silica is cobalt-free and turns dark green when it's full of moisture. We'd pick orange every time, especially for something sitting in a room where we spend time.

The Two Silica Products We Use

We use both packets and loose beads from Dry & Dry. Both are orange indicating, cobalt-free, and rechargeable in the microwave.

Rechargeable silica gel packets

Dry and Dry rechargeable orange indicating silica gel packets

These 20-gram packets come 30 to a bag. Each one has mostly white silica beads mixed with a few orange indicator beads that turn dark green when the packet is full.

Where we use them: in the spare spaces inside the AMS, and one in each vacuum-seal bag with our extra spools.
Coverage: the listing says each packet covers about 2,400 cubic inches.
Recharging: microwave for 2 to 5 minutes, or bake at 200 to 250°F for 30 minutes to 2 hours, per the listing. The packet material is sturdy enough to go in the microwave.
Comes in a resealable bag, so the spares stay fresh until you need them.

With 30 in a bag, we have plenty to rotate. While one set is recharging, a fresh set goes in the AMS.

See the Rechargeable Silica Gel Packets on Amazon

Orange indicating silica gel beads

We also bought a 1-quart jug (about 2 pounds) of loose beads to fill our printed desiccant boxes. Since you can see every bead, it's easy to tell at a glance when they need recharging.

Bead size: 3 to 5 mm, which is the standard size and fits nicely in AMS desiccant boxes.
Color change: orange when fresh, dark green when saturated. The listing says they turn green when they're about 50 to 60% full, so there's still some capacity left when you notice.
Recharging: microwave for about 10 minutes on defrost, or bake at 200 to 250°F for 30 minutes to 2 hours. Don't go over 250°F.
Storage: the jug seals airtight, so the extra beads stay dry between refills.

See the Silica Gel Beads on Amazon

The Printed Boxes That Hold the Silica

Loose beads need a container, and this is where printing your own accessories is fun. We printed the SPILLPROOF AMS Desiccant Box by Joey Lopez Design from MakerWorld. It's free, hugely popular, and it fits right in the front of the AMS, between the filament feeders.

Why we like it:

It won't spill. The lids slide on and snap closed, and they're designed so they can't pop open inside the AMS. The last thing you want is silica beads rolling around your feeders.
It uses wasted space. That spot between the feeders is otherwise empty, so you get more desiccant in the AMS without giving anything up.
There's room for a hygrometer. This version has a spot for a small round hygrometer, if you'd like a second humidity reading you can see right through the AMS lid. There are versions for other hygrometer shapes too, plus one with no hygrometer at all.
You can double up. The designer notes that the larger middle boxes can be doubled, one behind the other, for even more silica.
It's easy to print. Open it in the Bambu Handy app or Bambu Studio, pick the print profile for your printer, and send it.

One note: this version is made for the original AMS. The designer says AMS 2 Pro versions are coming separately as "SPILLPROOF 2."

How to Recharge Silica Gel

When most of the orange has turned dark green, it's time to recharge. Always follow the instructions on your silica, but here's the general idea:

Take the silica out of anything printed. PLA starts to soften at around 140°F, so never put your printed boxes in the microwave or oven. Pour the beads into a microwave-safe dish.
Heat it. For our beads, that's about 10 minutes on defrost. For the packets, it's 2 to 5 minutes. Short bursts with a quick stir in between help it heat evenly.
Check the color. When the beads are back to orange, they're done.
Let it cool completely. Hot silica can be very hot to the touch, and warm silica doesn't absorb moisture well. Let it cool in a sealed container so it doesn't start soaking up room air right away.
Put it back in the boxes and the AMS, and close the lid.

Tip: keep a second batch ready. We swap in fresh silica right away and recharge the used batch when we have a few minutes.

Our Results: From D to A

Here's what our setup looks like now:

The desiccant packets that came with the AMS, taken out of their plastic bags (they ship sealed, and they can't absorb anything until you unwrap them)
Rechargeable silica packets tucked into the spare spaces in the AMS
Printed SPILLPROOF boxes filled with orange silica beads across the front, between the feeders

With just the included packets, our AMS read "D." With everything above, it climbed to "A," and it stays there as long as we recharge the silica when it turns green.

More Tips for Keeping Filament Dry

Keep the AMS lid closed as much as you can, and close it right after swapping spools.
Check the humidity letter in the app every so often. If it starts creeping up, it's time to recharge.
Store spare spools in vacuum-seal bags with a silica packet in each one. They take up less room, and they stay dry until you need them.
Put new filament away quickly. Most spools come in a sealed bag with a desiccant packet. Leave them sealed until you're ready to use them.

Silica Gel and AMS FAQ

Will silica gel dry out filament that's already wet?

Not really. Silica is great at keeping dry filament dry, but it works too slowly to rescue a spool that's already soaked up a lot of moisture. For that, you'll want a filament dryer. Once it's dry, silica keeps it that way.

How often do I need to recharge it?

It depends on how humid your home is and how often you open the AMS. With indicating silica, you don't have to guess. Recharge it when most of the beads have turned dark green.

Can I recharge the packets that came with the AMS?

No. Those aren't made to be recharged. Use them until they're spent, then switch to rechargeable silica.

Is silica gel safe?

Silica gel is non-toxic and chemically inert, but it isn't food. Keep it away from kids and pets, just like the "Do Not Eat" label says. Choose orange indicating silica over blue to avoid cobalt chloride.

The Bottom Line

If your AMS humidity reading isn't an A or B, the desiccant that came with it probably isn't enough. A bag of rechargeable silica packets, a jug of orange beads and a few free printed boxes fixed it for us, and since the silica recharges in the microwave, we don't have to keep buying new desiccant.

See the Rechargeable Silica Gel Packets on Amazon

See the Silica Gel Beads on Amazon