I've got some good quality "carpet" underlay 9mm thick with foil backing, left over from carpeting other rooms. Would this be ok to use on top of ceramic tiled floor, underneath wood/laminate flooring?
No.
Underlayment for carpet is very different than underlayment for wooden/melamine laminated flooring.
For one the carpet underlayment will disintegrate over the years because the compact flooring ontop of it will prevent it from 'breathing' as it can with carpet.
Secondly, always use materials specifically made for the specific job/purpose to prevent problems/damages etc.
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