[Default] On Fri, 16 Jul 2010 06:15:52 -0700 (PDT), a certain
chimpanzee, ransley , randomly hit the
keyboard and wrote:

Polyisocyanurate has the highest R value pf 7.2" initialy, it is rated
here at R6.7 or so as it looses some R value as it cures, its the
product that is foil faced here in the US. Polystyrene is about
R5"-5.5", and the white foamboard R 4-4.5" With the added value of a
foil radiant barrier Polyisocyanurate is the best beal. Liqued foams
are the same, they vary depending on type from R4 - R 7 per inch

In SI units, polyisocyanurate (PIR) has a conductivity value (k-value)
of 0.023W/mK. Divide the thickness by the k-value to get the R-value,
so 50mm thickness gives an R-value of 2.17m^2K/W.

American R-values are effectively resistivity values, as they are
expressed as Rnn per inch, which is a) a little misleading and b) not
entirely accurate, as some materials have different resistances as
they get thicker.
--
Hugo Nebula
"If no-one on the internet wants a piece of this,
just how far from the pack have I strayed"?