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Shipping containers were never designed for human comfort.
They are thin steel shells. Steel has high thermal conductivity. It responds fast to temperature swings.
In Australia, that means:
When warm, moisture-laden air hits a cold steel surface, it drops below dew point. Water forms. Drips. Soaks linings. Rust begins.
That is condensation.
Traditional response?
Fill the cavity with bulk insulation. Batts, foam boards, spray foam.
But containers are different.
They are:
The core issue is not just insulation value.
It is surface temperature control.
Condensation forms when surface temperature falls below the dew point temperature of internal air.
Two drivers dominate in containers:
During the day, steel absorbs solar radiation across UV, visible and near-infrared wavelengths. According to the U.S. Department of Energy, solar radiation is the primary source of heat gain in metal roofs and walls
https://www.energy.gov/energysaver/cool-roofs
Steel heats rapidly. Internal air warms. Moisture levels increase.
At night, that same steel rapidly loses heat through long-wave infrared radiation to the sky. This phenomenon is known as radiative cooling.
https://www.sciencedirect.com/topics/engineering/radiative-cooling
Because steel has high thermal diffusivity, it changes temperature quickly. The internal surface can fall below dew point in hours.
Bulk insulation slows heat transfer.
But it does not manage:
In fact, poorly detailed bulk insulation can trap moisture against steel, accelerating corrosion.
Corrosion under insulation is a known global issue in industrial sectors
https://www.nace.org/resources/corrosion-central/corrosion-101/corrosion-under-insulation
Containers are simply thin industrial steel boxes. The physics is identical.
Bulk insulation works by resisting conductive heat flow. It relies on thickness and trapped air.
Containers present three problems:
1. Minimal cavity depth
Space is limited. Every millimetre matters.
2. Thermal bridging
Steel ribs act as direct conductive pathways. Even high R-value batts do not stop bridging through structural members.
3. Moisture risk
If the steel surface behind insulation drops below dew point, condensation forms unseen. Over time, rust develops from the inside out.
Spray foam reduces air gaps, but it still does not address solar radiation loading on the outer steel surface. It reacts after heat has already entered the structure.
You are insulating against a problem that could have been stopped at the surface.
The smarter strategy is controlling the steel temperature itself.
If you stabilise the external surface temperature, you reduce:
This is where high-performance ceramic heat-blocking coatings come into play.
Rather than adding thickness internally, you modify the external thermal behaviour of the steel.
Key mechanisms include:
Research into cool roof materials confirms that reflective and emissive surfaces significantly reduce heat load and surface temperature
https://coolroofs.org/documents/Cool_Roof_Guide.pdf
By limiting solar absorption, you prevent the steel from reaching extreme temperatures during the day.
By managing emissivity and diffusivity, you reduce extreme temperature drops at night.
The result is a narrower thermal swing.
And condensation is driven by rapid thermal swing.
A container coated externally with a ceramic heat-blocking system behaves differently.
Instead of acting as a thin hot plate in the sun and a cold plate at night, it becomes a moderated envelope.
Surface temperature is stabilised.
Internal air temperature becomes more consistent.
Steel is less likely to fall below dew point because:
This reduces the conditions required for condensation formation.
For container offices, homes, remote mining accommodation, site sheds, and modular classrooms, this shift is critical.
You are not just insulating.
You are controlling surface physics.
Condensation inside containers does more than damage linings.
It attacks the steel.
Repeated wetting and drying cycles accelerate corrosion.
The World Corrosion Organization estimates corrosion costs economies over 3% of GDP annually
https://www.worldcorrosion.org/what-is-corrosion
In a container, internal rust often begins where insulation traps moisture. It is hidden until structural damage appears.
Managing condensation at the surface level protects:
For container builds, the most effective approach is layered but surface-led:
The coating becomes the first line of defence.
It changes the equation before moisture forms.
Instead of fighting condensation after it appears, you prevent the thermal conditions that create it.
Traditional bulk insulation treats containers like framed houses.
They are not.
They are thin steel structures exposed to extreme solar radiation and rapid radiative cooling.
Condensation in containers is primarily a surface temperature problem.
Solve the surface behaviour, and you dramatically reduce the moisture risk.
Control radiation.
Control thermal swing.
Protect the steel.
That is the smarter path.
U.S. Department of Energy – Cool Roofs
https://www.energy.gov/energysaver/cool-roofs
Cool Roof Rating Council Guide
https://coolroofs.org/documents/Cool_Roof_Guide.pdf
ScienceDirect – Radiative Cooling
https://www.sciencedirect.com/topics/engineering/radiative-cooling
NACE – Corrosion Under Insulation
https://www.nace.org/resources/corrosion-central/corrosion-101/corrosion-under-insulation
World Corrosion Organization
https://www.worldcorrosion.org/what-is-corrosion
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