A purge tower is a block of filament that a multicolor 3D printer prints beside your model to clear the previous color out of its nozzle. Every time a single-nozzle printer changes color, it pushes leftover filament through the nozzle onto the tower until only the new color comes out. That filament is waste.
If you've ever watched a multicolor print and wondered what the tall, ugly stack next to your model is for, this is it. Here's how it works, why it costs so much, and what actually reduces it.
What Is a Purge Tower?
A purge tower (some slicers call it a prime tower or wipe tower) is a sacrificial structure printed alongside your model. Its job is to give the printer somewhere to dump filament that isn't clean.
It exists because of one physical limit: a nozzle can only hold one filament at a time, and the melted plastic inside it doesn't disappear when you swap filaments.
Why Single-Nozzle Printers Need One
On a printer with one nozzle, a color change looks like this:
- The printer retracts and unloads the current filament.
- The next filament is loaded into the hotend.
- The nozzle is still full of the previous color.
- The printer extrudes until the old color is flushed out and the new color runs clean.
Step 4 is the purge. If it stops too early, you get the old color streaking into your model. So the printer errs on the side of pushing out more, and that material lands on the purge tower, in a purge bin, or inside the model's infill, depending on the printer and slicer.
Where the Purged Filament Goes
Depending on the system, the waste ends up in one of three places:
- On a purge tower printed next to the model.
- In a waste chute or bin, as the loose strands and blobs many people call "poop."
- Inside the model itself, when the slicer is set to flush into infill or supports.
Using infill or supports reduces the visible pile, but the filament is still spent on something that isn't your part. And only some of it can be reused.
Why the Waste Adds Up So Fast
Purge volume depends on the number of color changes and on how hard each change is. These factors drive it:
- Number of color changes. Every layer where the color switches can trigger another purge.
- Color jump. Going from dark to light usually takes more flushing than light to dark, because a trace of dark pigment shows.
- Nozzle volume. More melted plastic in the nozzle means more to push out.
- Material differences. Switching between materials with different temperatures needs more clearing, not less.
On a model with many colors and layers, the waste can be larger than the model itself. That's why a small, colorful print can leave a surprisingly large pile.
How to Reduce Purge Waste on a Single-Nozzle Printer
There are real ways to cut it, and they're worth using:
- Reduce color changes. Fewer layers where the color switches means fewer purges.
- Lower the flush volume for color pairs that are close together.
- Flush into infill or supports so the waste does some work.
- Shrink or reposition the tower where the slicer allows it.
These help. But they all work around the same constraint: the colors share a nozzle. You can purge less, but you can't remove the reason for purging.
The Architectural Fix: One Nozzle per Color
The way to remove the purge is to stop sharing the nozzle. If every filament has its own nozzle, there's no previous color to clear out.
Several designs do this: fixed multi-extruder printers, tool changers that pick up and put down heads, and independent toolhead printers where every head stays on the machine. They differ in how the heads move, how they park, and how much has to be calibrated, but they all share the same idea: separate nozzles instead of one shared hotend.
Quadro is built this way. It has four independent toolheads on a single axis, each with its own filament and its own nozzle. A color change means switching toolheads, not flushing a nozzle. Read the full explanation in Why Quadro Doesn't Purge.
Is a Priming Tower the Same as a Purge Tower?
Not quite. A purge tower clears the previous color from a shared nozzle. A priming tower stabilizes extrusion pressure when a toolhead that's been idle starts printing again. The structure can look similar. The reason it exists, and the amount of filament it uses, is different. We explain the difference in Why Quadro Doesn't Purge.
Key Takeaways
- A purge tower clears the old color from a shared nozzle after a color change.
- The waste grows with the number of color changes and the contrast between colors.
- You can reduce it with smarter slicing, but not remove it on a single nozzle.
- Giving each color its own nozzle removes the reason to purge.
Ready to print multicolor without the pile? Back Quadro on Kickstarter or reserve yours for $20. Reservations are fully refundable.
3. FAQ
What is a purge tower in 3D printing? A purge tower is a sacrificial structure printed next to your model. A single-nozzle multicolor printer pushes leftover filament onto it after each color change to clear the old color out of the nozzle.
Is a purge tower the same as a prime tower? Usually, yes. Different slicers use "purge tower," "prime tower," or "wipe tower" for the same structure. It's used to flush and prime the nozzle after a color or material change.
Why do multicolor prints waste so much filament? Because one nozzle holds one filament at a time. Each color change requires flushing the previous color out, and the amount grows with the number of changes and the contrast between colors.
Can you print multicolor without a purge tower? You can reduce it by flushing into infill or supports, but on a single-nozzle printer something still has to be flushed. Printers with one nozzle per color don't need to clear a previous color, so they don't need a color-clearing purge.
Does Quadro use a purge tower? No. Quadro prints a small priming tower that stabilizes extrusion pressure when a toolhead becomes active again. It doesn't clear one color out of a shared nozzle, because Quadro's colors never share a nozzle.
