Andy Wade wrote:

The Natural Philosopher wrote:

Even 3mm of foam is a heck of a sight better than 9" of brick.


Wrong. Thermal resistance (R-value) is thickness divided by the thermal
conductivity of the material: R = t/k.

- for 3mm foam: t = 0.003m, k = 0.03 W/mK typically,
hence R = 0.1 m^2K/W approx.

- for 9 in. brick: t = 0.225 m, k ~ 1 W/mK,
hence R = 0.2 m^2K/W approx.

So 9 in. of brick is about twice as good as 3mm of foam, so far as
steady state heat loss is concerned.


Umm. let's rephrase that rather sloppy sentence.

"Even 3mm of foam on 9" of solid brick is better than no foam at all"

The remark was prompted by the fact that lining just such a wall with
3mm cork tiles - and in fact it may actually have been 4.5" brick - made
a HUGE difference.