Any news on PTFE alternatives?

Hi,

I was wondering if there is progress on alternatives to PTFE used in hotends. Replacing PTFE liners with glass tubes or zirconium tubes would allow us to use higher printing temperatures that are not achievable using PTFE. I've found some old topics discussing this but didn't hear or see a commercial/non-commercial working example. There is a vendor on Aliexpress who sells glass tubes or zirconium tubes with configurable inner and outer diameter but they do have minimal order quantities, so I can't experiment with them.

Thanks...

What's wrong with bare metal? I thought ptfe was only really useful for pla, and even there it's not essential. My 3mm setup doesn't use any liner material. I haven't tried PC which I guess is the main high temperature candidate - does that have problems without a liner?