I was scrolling Amazon, searching for ceramic heaters when I stumbled upon a ceramic heatbreak, which is not something I've seen before.

I thought ceramics would be too heat conductive (I mean, they make heaters with it) and too fragile to work, but if it's not the case, it would make a lot of sense since ceramic bearings have even lower friction than stainless steel ones, so perhaps that low friction translates to polymers. I did more searching on AliExpress and found out that Fysetc  and Trianglelab both make such heatbreaks, and I was surprised to find out how low the thermal conductivity is:

The first tubes I found were low-cost but also had a matte surface finish. I then found some precision polished zirconia tubes in a variety of sizes, most notably 2x4x16mm and 2.05x3x25mm.

I looked into it and, as I probably should've known, "ceramics" is about as precise as saying something is made of "metal" or "plastic". On AliExpress, there seem to be 2 types: Alumina and Zirconia. The former is 10x more heat conductive at 27 W/(m.K). NF goes one step beyond and uses "aerospace materials" for their NF Zone, which has a removeable black heatbreak so I don't even know what it could be:

On AliExpress, there are also quartz capillary tubes which might be a cheaper alternative that has a similarly low thermal conductivity, but they likely would be too fragile.