Normal PVC insulated wiring inside flexible plastic tubing. Of course using products designed and certified for this.
There is no need for special fire-proof materials, nor they are required almost anywhere AFAIK. This is because properly sized and fused wiring just simply has no mechanism to overheat and set things on fire. Note though that law requires certified professionals to do the planning and perform the installations.
The key is to understand that the distribution box fuse size defines the copper gauge, this is a simple table lookup. Larger wire area is required when the wiring is run inside thermal insulation materials.
Note that the required cross-sectional areas are quite a bit more than the classical "rules of thumb", because first, fuses are not precision devices so a 16A fused circuit can carry up to 24A pretty much indefinitely, and 32A for quite some time (an hour, maybe), and then again, a typical house wiring consists of first PVC insulation around the wires, then another 1-2 layers of PVC outer sleeve, then air gap, then the flexible cable conduit, then more or less thermally insulating building materials. And it needs to last for decades without degradation so basically the PVC has to keep below about 60 degC. This is why 2.5mm^2 is very typical even for the circuits using smallest sensible fuse sizes.