The stuff used for insulating pipes, The glass fibre stuff wraped in silver foil. Would this be ne good for insulating exhuasts? Im more thinking of just using the outer foil to wrap my lagged sections to stop them geting wet. Opinions?

 

You can get special heat wrap paint called Hi-Heat Coating which waterproofs and binds the surface. DEI do it, you can get it out of the Demon Tweeks catalogue. Comes in either silver or black and IIRC it's about £10-£15 a can which is enough to do a hell of a lot of pipework.

As far as the silver foil idea goes, I'm not sure whether you're talking about wanting to keep heat in your pipes, or water out, or both?