Today I shipped out a hot-end, for testing, that had a liner made out of Rulon instead of PTFE. Rulon is supposed to be very similar to PTFE. However, it is rated for a temperature up to 288 degrees Celsius.
I figured I would have it tested as some users have reported PTFE degradation, at the hot-end, after months of heavy use. While the PTFE liners are fairly easy to replace, I figured that it wouldn't hurt to test other materials.
Even if this material is initially successful, many questions will still remain.