May 2024

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LOW LAMDA INSULANTS: FAQS
This month the team at A. Proctor Group compare low lamda insulants, focusing on aerogel
and rigid foam solutions...
In terms of thermal efficiency, aerogel
insulation and low lambda foam insulation
boards (like PIR and phenolic) perform very
similarly. But comparing them on thermal
performance alone, without taking into
consideration their other properties, is like saying
apples and oranges are similar because they are
both round fruits.
Aerogel and low lambda rigid foams are both
excellent insulators, but also very different in
other ways. In this month’s FAQs, the A.Proctor
Group looks at the performance characteristics
that set these low-lambda insulation solutions
apart.
What is the thermal conductivity of
aerogel and low lambda foam insulants?
Typical thermal conductivities range from 0.020
W/mK for aerogel and phenolic insulation, to
0.022 W/mK for a typical PIR foam board.
This range is lower – and therefore more
thermally efficient – than most other commonlyused
insulation types. The similarity in
performance means all of the products offer a
similar thermal benefit for similar thicknesses.
Precise lambda values can vary by manufacturer.
For example, A.Proctor Group’s aerogel blanket
product, Spacetherm A1, has a thermal
conductivity of 0.0195 W/mK.
What are the advantages of this thermal
efficiency?
The low lambda of rigid insulation products like
PIR and phenolic allows better U-values to be
achieved in constructions for which the products
are typically offered, including floors, walls and
roofs.
However, in solid wall applications, an air gap is
Installing Spacetherm from A Proctor Group.
often required due to the fact that the thermal
performance is detrimentally affected by being
installed to a potentially more moisture sensitive
substrate. In addition, the lowest U-values
offered by rigid boards often depend on the
insulation’s foil facing delivering a low emissivity
benefit in an adjacent air space.
Aerogel insulation is inherently hydrophobic,
meaning it is completely inert to the effects of
moisture. This means it can be fixed directly to
solid, and cavity, walls without compromising
thermal performance or damaging the insulation.
And because aerogel has no foil facing to provide
an enhanced low emissivity cavity, no air space is
required for the insulation to face into.
The unique composition of aerogel means it can
help to deliver thermal efficiency in spacecritical
areas where ‘conventional’ insulation
products are simply too thick.
The material is generally manufactured in 5-
10mm thicknesses, which can be layered to suit
the required thermal performance. These thin
layers make insulation possible in applications
where foam boards cannot be supplied at the
thickness required.
Using aerogel, the thermal performance of
ventilated facades can be enhanced generally, as
can areas of thermal bridge detailing such as
window reveals and steel beams.
Are aerogel’s moisture characteristics
important for solid wall constructions?
Moisture management in buildings is critical to
longevity of the building fabric and achieving the
intended performance from building elements.
Insulation materials therefore have to be selected
not just for their thermal performance, but also to
support good moisture management.
In new build, timber, steel and concrete framed
buildings, as well as more traditional cavity wall
constructions, the constructions are less moisture
sensitive. This allows greater flexibility in the type
and physical properties of the insulation. Foam
insulants are more than suitable for use as the
constructions benefit from a low permeability
insulation to reduce the amount of vapour that
can pass through the construction.
This is not the case with historic, solid brick and
stone buildings, however. In historic solid
masonry walls, we can have a lot of influence on
the way moisture moves due to both external and
internal conditions.
Solid walls are heavily influenced by driving rain
on the outside, often allowing quite a bit of
natural moisture penetration. The effect of this is
heavily tempered by the internal heat driving or
drying the moisture out of the wall. This allows
these walls to reach a seasonal equilibrium that
has allowed them to stand, in some cases, for
several hundred years.
Installing insulation and other energy efficiency
measures affects the building physics of the wall.
For example, adding insulation can keep the
interior warmer and cut fuel costs, but it can also
mean the walls are now significantly colder than
they have ever been due to not getting any heat to
them to help drive out the moisture. This can
result in interstitial condensation or moisture
46 TC MAY 2024