Just thought I'd share this info with everyone. I've just added
a Dormer to a new upstairs room. Basically 4" x 2" (95mm x 45mm) stud
walls. I've 'stuffed' it with the following insulation called Rocksilk
by Knauf. The spec. sheet gives the following details...

UNIVERSAL SLAB RS45
Thickness 100mm (I have also used 75mm)
Length: 1200mm
Width: 600mm
Area per pack (m^2): 3.6
Lamda (W/mK): 0.035
R Value (m^2K/W): 2.85
Fire ClassSlabs per Pack: A1
Pack per Pallet: 5
Product Code: 2361392

The price for one pack from Sheffield Insulations in Aberdeen
was £32. So that's nearly £10 per square metre. Quite expensive for
what it is.
It is good to work with, easily cut with a breadknife. Just
cut it about a quarter inch oversize and push between the studs.

Chris.