Hot pipe to shower valve buried in chased concrete wall. How should I insulate it?

[Peter]

I am installing a hot pipe to a concealed shower valve which runs for about 2m through a concrete wall. I have chased a 28mm channel for the pipe. How should I insulate this pipe? I have been considering wrapping it with a spiral of glass wool, if I can find that in strip form on a reel. Any other suggestions?

[dennis]

I would run it through a larger plastic pipe (6mm+ larger). The air gap should insulate it and provide room for expansion.