May 2019 • BuildingProducts.co.uk 41
Mitigating heat absorption
So what is the science behind the reflecting pigment
technology? All sunlight absorbed by an object is
converted to thermal energy and will increase its heat.
The more solar energy is absorbed, the greater the heat
build-up. Objects in direct, intense sunlight will heat up
more rapidly than those in the shadow.
As white reflects light, white products remain cooler,
so traditionally it was the preferred colour choice in
warmer climates. But white doesn’t always satisfy
customers demand, with aesthetically pleasing darker
colours increasingly required, which depending on their
pigmentation absorb solar energy and will get warm.
For this reason the pigmentation system needs to be
carefully examined. The visible spectra accounts for 41% of
the light but the amount reflected is fixed by the colour.
The largest part of the radiation however, (56%)
is the invisible infra-red sector and this is
where significant changes can be made by
selecting pigments with high reflectance –
hence low absorption but still meeting the
colour requirements in the visible spectra.
Pigments absorb some wavelengths of
guttering can reach
50 oC+ in the south
light and reflect others, which in the visible
spectra, results in the colours we see. In
extreme cases where all the wavelengths
are reflected, this is perceived as white and
if all is absorbed, as black. A colour that absorbs
some wavelengths and reflects others will appear
coloured and the perceived colour is dependent on the
wavelengths of the reflected light.
This mechanism of absorbing and reflecting isn’t
limited to the wavelengths in the visible spectra, it occurs
in the non-visible spectra and especially the part we are
interested in, the infra-red.
Reflecting pigments are tailored to reflect the
maximum amount of infra-red, yet still absorb the same
level of visible light in the visible spectra. This reduces the
absorbed radiation and is known as passive mitigation of
solar induced heat build-up.
Colours using this technology can offer up to a 40%
reduction in operating temperature profiles compared
to an identical colour formulated with conventional
pigments, resulting in lower service temperatures of the
Total Solar Reflectance
When selecting a reflecting pigment, the most important
factor is its total solar reflectance (TSR) value. At Colour
Tone Masterbatch we have an extensive library of
reflecting pigments we test to select the right products to
achieve an enhanced reflectance value.
Another test value we use is ‘heat build-up’, this is
where we measure the rise in temperature above the
ambient of a carbon black test piece, exposed to an
infrared heat source compared to one with a reflecting
Once we have designed a colour to match the one
specified, other considerations regarding pigment
performance must be taken into account.
Building applications for example, usually
require good light fastness and strong
By lowering the infrared energy absorbed,
the expansion and contraction that occurs
due to an increase in temperature in direct
sunlight will also reduce. This may not
sound significant, but we are all familiar with
the noise of black rainwater goods expanding on a
hot summer’s day.
Black PVC guttering for example, can easily reach
temperatures of 50ºC+ in the south of England. This isn’t
limited to black products either, brown and grey performs
similarly. Other products that suffer from thermal
expansion and contraction include roof tiles, soffits,
sidings and ridge tiles where expansion gaps have to be
left that may not be appropriate for the application.
By decreasing the demand on the heat stabiliser in the
polymer compound, it can help prevent product failure
which manifests itself as discolouration, loss of gloss,
crazing of the surface and in extreme cases embrittlement
and reduced physical properties – to significantly extend
its service life.
Chalking is another common problem which occurs
in all plastics to some extent when the polymer surface
breaks down, allowing the ingress of moisture which
exposes the chalk talc and/or TiO2 contained in the
polymer formulation. By using ‘cool plastics’ and reducing
the surface temperature this reaction is slowed, resulting
in less chalking and a better long-term appearance.
It is obvious then that significant environmental,
energy saving and performance benefits can be gained
from ‘cool plastics’– so the real question isn’t whether we
should adopt building products featuring this technology,
but why we haven’t done it sooner?
tailored to reflect
amount of infra-red,
yet still absorb
the same level of
visible light in the
This reduces the
and is known as
passive mitigation of
solar induced heat