B&Q do a grey foam one in a roll, which is rather more expensive than the paper-thin white one, although still pretty reasonable. It's called 'Combilay'. I've used it extensively in my house, and have found it very good both for its underlay and noise deadening properties. The only one I have used that was a little better quality than this, was some green 'professional grade' stuff that was obtained for me at trade price direct from the warehouse, by a carpet fitter mate. Proper retail price was TTP ...
It was just slightly easier to lay, because it had a self adhesive strip and a plastic sheet joining overhang at the sides.
I used 2 types on my floor. The cheap white stuff over heavy guage DPC plastic, but then I managed to find some black rubberised u'lay with a silver foil backing for the hall. The hall is much better deadened.
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