plus its a pointless feking spec anyway, good for timber yes but u-value is never accurate or anywhere near good as it should be. if its minus 20 outside it will at least minus 10 in the cavity cold air behind the insulation ? ? ? against the building you are trying to keep warm ? ? ? ? ? ?
you dont want any old bugger fitting it either it needs care at windows/openings stops etc.
Ive done loads of it mate, not touched it for about three yrs and hope never will again
have I done enough to put you off yet?