Insulating under the attic floor?

[Reesy]

Here's a poser:
I'd like to improve the insulation under my attic boards. There's a 4" gap under the boards, with fibreglass in it. Any suggestions for thin insulation materials - the equivalent of 6" / 150mm insulation or so? Ideally I'd like it physically strong enough so I can cover the joists & not get compressed, to get rid of the thermal bridges. I'd rather not add more joists if I can get away with it. Thanks!

[Deluks]

Seems a bit pointless to me. You already have an insulated, boarded out loft, why make more work for yourself? The boards themselves will insulate as well to a certain extent.
The only thing to suggest would be to rip out the floor, cross batten and add thicker insulation, before boarding up again. I'm not going into details though, there are plenty of recent posts explaining this procedure.

[JohnD]

"...thin insulation materials - the equivalent of 6" / 150mm insulation ..."

If you could get a one-inch insulation that was equivalent to six inches, we'd all be using it.To get six inches of insulation, youy need to use six inches.