High performance insulation

[lalalonglegs]

I want to insulate the ceilings in a bedroom built into an attic. If I use the full 270mm recommended by building regs then it will really impede on the ceiling height - are there any thinner types of insulation that have good U-values (I can never remember if U-values should be high or low to be desirable )?

Celotex and kingspan are better insulators than mineral wool quilt. You only need something like half the thickness. They are rigid boards. Have a look at their websites.