It seems quite hard to get 6mm pipe insulation for 22mm pipe. Even
Armaflex don't go that thin above 15mm pipe.

Found some (Alfaflex red sleeved):

http://plumbing4home.com/10-meters-o...wrap-6mm-thick


But I wonder why it's so uncommon...? If you use Talon clips (common)
stacked, you get 35mm of space around a 22mm = 13/2 - 7.5mm thickness.

Even at such a thin wall thickness, online calcs show it roughly halves
heat loss.