"Peter" wrote in message
...
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?

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