A 25mm sheet of this stuff claims to be equivalent to 80mm of Celotex or
200mm of rockwool. Easy to install as well. Sounds too good to be true. Is
it any good?
I haven't used it, but I notice that the U value calculation was based on a
structure that had a 25mm airgap on each side of the insulating material.
This would give the material the best opportunity for its reflective properties
to work but means that to get the best effect you require a 75mm cavity
and a structure to support the material in the middle.
I haven't looked at the U value measurement method for celotex, but I bet it
doesn't contain such a restriction.
Plus a quote from a Eurima journal (the mineral wool body, so don't expect
For anyone contemplating the use of a reflective foil insulation
Eurima can do no better than to repeat the advice offered by Peter
Warm, energy consultant, in his article 'Reflective, thin insulations-
winners or loosers?' viz.,
o Be cynical about claims for tests results unless they have been
carried out to BS 874 in a hot box method
o Combined Reflective/ Convective insulation such as that marketed by
ACTIS should have a lower conductivity than air based products fibre
products, but not 6 times lower. I assume 1.5 times lower i.e. a k
value of 0.027 W/mK but add in the requirement for a clear 20mm cavity
on either side, which reduces the effective thickness that can be
o I account for all thermal bridging. Thermal bridging and radiation
is critical in radiation insulation because it can completely destroy
the insulation value locally around the thermal bridge
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