Pipe insulation - the best material?

[flipper]

Have just bought a bungalow with long pipe runs between boiler and HW cylinder / rads and need to close off every available opportunity for heat loss to avoid astronomical heating bills. As the lagging is pretty poor in places and I can't afford to re-plumb, what are the best options (material, thickness, etc) for covering the pipes please - all opinions welcome! :-)

[plumbbob]

This has to be an industry favourite.

http://www.screwfix.com/prods/10943/Plu ... m-50m-Pack

Price is for 50 metres you will find smaller quantities from any local plumber's merchant.