Thinner Loft insulation

[John Fox]

I want to update my loft insulation but all of the quotes I've had are for 10 -12cm thick fabric.
I want to keep the loft for storage and am told that it's not a good idea to squash to insulation with boards as it reduces the efficiency.
Is there an alternative that would sit within the depth of the rafters and be efficient?
I have seen insulation with what looks like a foil backing and wondered if anyone has experience of it and could recommend it or something else.

[buildersmate]

You could use polyurethane rigid board. Kingspean and Celotex were the market leaders in these products but there are a number of others around. They are backed each side with silver foil and maybe are what you have seen. They are approximately twice as efficient as fibreglass roll in U-value (thermal insulation measure) so an 80mm thickness to fit between your roof truss horizontal would be equivalent to 160mm of fibreglass.

[John Fox]

Thank you. I'll get some on order.