Celotex GA3080 (80mm thick) is on sale from
The R value is given as 3.45 m.sq.K/W and the U value as 0.29 W/m.sq.K.
I have consulted Wikipedia at
So:
(1) the R values look about right from the Wikipedia examples - and the Celotex comes up as about twice as effective as the fibreglass per unit of thickness. (2) The fibreglass is about 1/5 the cost of Celotex for the same R value (and this is from a discount Celotex web site).
So my one remaining problem is the U value. If the U value is the reciprocal of the R value then for the same R value shouldn't you have the same U value? And if the R values are similar shouldn't the U values be similar? Quick check with the calculator for 1/R shows that the Knauff figures are wildly off. Should have an R value of about 22.7!
I have checked another site
O.K. - dodgy (but consistent) figures from Knauff.
Strong cost justification for buying the space blanket which is no doubt subsidised by me paying my heating bills.
Longer note than I intended - got baffled by U values part way through!
Cheers
Dave R