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The insulation industry has trained everyone to think from the inside out.
R-values. Bulk batts. Thickness. Trapped air.
But solar heat does not start inside a building.
It starts at the surface.
If you want performance, you need to understand the difference between surface behaviour control and internal insulation resistance.
Solar energy hitting a roof is made up of:
Reference:
NASA Earth Observatory – Solar Radiation Basics
https://earthobservatory.nasa.gov/features/EnergyBalance
Most of that energy is infrared. That is the heat load.
If the surface absorbs it, the substrate temperature rises dramatically.
Once that happens, internal insulation is reacting to stored heat, not preventing it.
That is a big difference.
Bulk insulation works by resisting conductive heat transfer. It traps air. It slows heat flow.
Standards like AS/NZS 4859.1 and ASTM C518 measure conductivity and thermal resistance under controlled conditions.
ASTM C518 – Standard Test Method for Steady-State Thermal Transmission Properties
https://www.astm.org/c0518
The problem is this:
Internal insulation reduces the rate of heat moving inside.
It does not stop the surface from overheating.
That is why roof cavities can exceed 60°C to 80°C in Australian summer conditions.
CSIRO guidance on roof space temperatures:
https://www.csiro.au/en/research/environmental-impacts/climate-change/climate-adaptation/keeping-homes-cool
By the time heat reaches the insulation layer, the damage is done.
Surface behaviour focuses on three core physics principles:
Reflectance prevents absorption.
Emissivity releases residual heat.
Low diffusivity prevents rapid heat migration into the substrate.
This is not about slowing heat inside a wall.
It is about stopping heat loading at the envelope.
Lawrence Berkeley National Laboratory research on cool surfaces confirms the importance of solar reflectance and thermal emittance in reducing roof temperature.
LBNL Heat Island Group – Cool Roofs Overview
https://heatisland.lbl.gov/coolscience/cool-roofs
But most reflective paints rely primarily on reflectance alone.
High reflectance without controlled diffusivity still allows substrate heat gain.
That is where surface science separates coatings from insulation systems.
Field performance matters more than lab theory.
The City of Adelaide Cool Roof Trial recorded internal temperature reductions of up to 6°C when using Super Therm®.
City of Adelaide Cool Roof Trial summary:
https://neotechcoatings.com/super-therm-testing-and-results/
The dry film thickness was only 0.25 mm.
That matters.
At 250 microns, the coating is not adding R-value in the traditional sense.
It is controlling surface heat load through reflectivity, emissivity and low thermal diffusivity.
ASTM E1461 testing confirms low thermal diffusivity values in thin materials.
ASTM E1461 – Thermal Diffusivity by Flash Method
https://www.astm.org/e1461
When heat cannot rapidly diffuse into the substrate, internal temperature stabilises.
Internal insulation cannot do that because it is not at the point of impact.
One of the biggest misconceptions is that reflective systems only work in summer.
Surface behaviour coatings that balance reflectance and emissivity can reduce peak heat gain in summer while moderating rapid radiative cooling at night.
Princeton research into radiative heat transfer differences between sky cooling and ground-level IR exchange highlights how infrared behaviour varies by wavelength and environment.
Princeton Engineering – Radiative Cooling Research
https://engineering.princeton.edu/news/2019/10/03/scientists-find-new-way-keep-buildings-cool-without-electricity
Internal insulation cannot respond to this dynamic surface exchange.
It is passive resistance.
Surface science is active control without energy use.
Be realistic.
Internal insulation is essential in cold climates for conductive heat loss reduction.
It is effective in walls and ceilings where solar radiation is not directly striking.
Surface behaviour control is critical in:
In high radiation climates like Australia, the surface becomes the battleground.
If you do not manage that, you are constantly fighting stored heat.
Here is the practical order of control:
Most buildings reverse this order.
That is inefficient.
Surface behaviour coatings like Super Therm® are designed to block 96.1% of total solar heat and reflect 97% of UV, with 99% infrared blocking performance verified through ASTM testing.
More detailed performance data:
https://neotechcoatings.com/coating-products/super-therm-solar-heat-block-coating/
This is not a paint claim.
It is surface heat load management.
| Factor | Internal Insulation | Surface Behaviour Coating |
|---|---|---|
| Location | Inside cavity | At heat impact point |
| Mechanism | Resist conduction | Block radiation + control diffusion |
| Solar IR Control | No | Yes |
| Dynamic Performance | Limited | High |
| Thickness Required | 50–200 mm | 0.25 mm dry film |
| Heat Storage in Substrate | High | Minimal |
Internal insulation slows heat movement.
Surface behaviour reduces heat existence in the first place.
If you are designing for thermal resilience in high solar regions, surface control is not optional.
It is fundamental.
NASA Earth Observatory – Solar Energy Balance
https://earthobservatory.nasa.gov/features/EnergyBalance
ASTM C518 – Thermal Transmission Properties
https://www.astm.org/c0518
ASTM E1461 – Thermal Diffusivity
https://www.astm.org/e1461
LBNL Heat Island Group – Cool Roof Science
https://heatisland.lbl.gov/coolscience/cool-roofs
Princeton Radiative Cooling Research
https://engineering.princeton.edu/news/2019/10/03/scientists-find-new-way-keep-buildings-cool-without-electricity
Super Therm® Testing and Results
https://neotechcoatings.com/super-therm-testing-and-results/
Super Therm® Product Page
https://neotechcoatings.com/coating-products/super-therm-solar-heat-block-coating/
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