Waste less Multi Color/Material Parts with any Printer

The Basic Idea

I spent a lot of time 3D printing shoes lately and a few months ago I came across this model of a 3D printable shoe by CloudBerry. The model is great and I've printed it multiple times now. Seeking to improve material consumption and comfort even more, I wanted to create a light and soft top and a rigid and durable sole. Of course you could just glue two parts together, but that would be kind of boring, right?

So it should be one print. In order for this to work, you will need a special formable filament. The different sections are printed with variable temperature to achieve different material properties. 

You can buy filament with dynamic foaming technology from different vendors either as PLA or TPU. I used Recreus Filaflex 95 Foamy Footwearology Edition, but there also other options (for example colorFabb varioShore)

In the case of the shoe I printed the sole with 230°C which results in a darker color and higher hardness (≈ Shore 95A) since the material is unfoamed. For the rest of the shoe, I used a nozzle temperature of 250°C. At this temperature little gas bubbles start to form inside the plastic and thus it starts to expand. To compensate for the increase in volume, I lowered the flow factor to 0,65. Foaming also causes the color to get lighter and significantly reduces its hardness (up to Shore 70A in my case).

That itself wasn't new (there are plenty of heat towers for material testing that illustrate the effect), but I wanted to make use of it in real, complex objects by changing the temperature in every layer.

How does it work?

I've only tried this with OrcaSlicer, so I'm going to use that process as an example.

First, enable the Single Extruder Multi Material checkbox in Printer Settings > Multi Material

Go to Machine G-code > Change filament G-code delete everything in this box.

Create two (or more) filament presets, one unfoamed (230°C nozzle temp; 1,0 extrusion multiplier) and one foamed (250°C nozzle temp; 0,65 extrusion multiplier). Of course you can add more in-between to achieve half-formed states.

Then, you just have to paint the object or add modifiers. 

Please let me know what you think about this. Does it also work for you? Or are there any problems or aspects I forgot to mention?