A standard ISO steel freight container under direct tropical sun is one of the most thermally demanding metal structures in regular logistical use. The surface-area-to-volume ratio is high, the thermal mass of the steel envelope is low, and unprotected metal panels under sustained solar radiation can raise internal temperatures beyond safe limits for cargo and equipment within hours of sunrise. Mechanical cooling controls internal temperature but compounds the energy problem: the lower a container’s thermal resistance, the harder the compressor must work - and the faster it degrades.
In July 2025, a four-day controlled field test conducted in Vietnam provided quantified, instrument-logged evidence of the thermal and energy performance difference between a 1 mm GWR NANO INSULATION® coating and an uninsulated steel surface.
Unrivalled efficiency against heat.
The coated container consumed 43.02% less cooling energy (kWh) on average over four days compared to the white-painted reference. Daily cooling energy savings peaked at 53.56% on 3 July 2025 (peak external temperature: 33.5 °C). The coated container maintained internal temperature within the 28 °C ±1 °C comfort setpoint throughout the measurement period; the reference container exceeded the setpoint by 3–6 °C during peak load hours.
Test Methodology
The study compared two structurally identical 20-foot (6.06 m) standard ISO steel freight containers fitted with the same model of air-conditioning unit - a COMFEE 05 Star Smart Air Conditioner (CFS-10VGPF) - operating at identical thermostat settings. One container received a 1 mm spray-applied coat of GWR NANO INSULATION® across its exterior surface. The second was left uninsulated and painted white - a configuration that reflects solar radiation more effectively than uncoated or dark steel, and which represents the best-performing passive baseline achievable without added insulation.
Both units were monitored under identical ambient conditions from 2 to 5 July 2025. Internal temperature was logged hourly via Tuya Zigbee humidity and temperature sensors. Daily energy consumption was recorded in kWh using Tuya WiFi Smart Energy Meters. The target internal temperature was 28 °C ±1 °C (27 °C ±1 °C on 2 July). Ambient temperatures ranged from 24.5 to 35 °C, with sustained temperatures consistently above 30 °C during working hours (08:00–17:00).
Measured Results
The results were consistent across all four test days. In every case, the GWR NANO INSULATION® container maintained internal temperatures within the target comfort band; the uninsulated container did not.
| Date | No GWR (kWh) | GWR Nano (kWh) | Savings (kWh) | Savings (%) |
|---|---|---|---|---|
| 2 July | 9.58 | 6.21 | 3.37 | 35.18% |
| 3 July | 7.58 | 3.52 | 4.06 | 53.56% |
| 4 July | 8.15 | 4.57 | 3.58 | 43.93% |
| 5 July | 9.67 | 5.63 | 4.04 | 41.78% |
| Total | 34.98 | 19.93 | 15.05 | 43.02% |
On 2 July - the most thermally demanding day of the test, with an external peak of 34.9 °C at 13:00 - the uninsulated container exceeded the target temperature for over four hours, with internal temperature reaching 33.8 °C: 5.8 °C above the 28 °C setpoint. The GWR NANO INSULATION® container held a maximum of 28.9 °C throughout the day, with the compressor cycling intermittently in short bursts.
On 3 July, at an external peak of 33.5 °C, the uninsulated container reached 31.5 °C internally despite continuous compressor operation. The GWR container’s internal temperature ranged between 25.5 and 28.9 °C throughout the day. Energy savings on this day peaked at 53.56% - the highest recorded value over the four-day test period.
On 4 July, the external peak was 34.4 °C with rapid morning heat build-up. The uninsulated container exceeded 32.0 °C and remained outside the comfort band for over six hours; the cooling system ran continuously without restoring target conditions. The GWR container reached 28.9 °C briefly on one occasion, then stabilised below the upper tolerance limit. Energy savings: 43.93%.
On 5 July, the external peak reached 34.8 °C with a sustained heat plateau through mid-afternoon. The uninsulated container peaked at 32.6 °C and was unable to return to the target range once overheated - a clear demonstration of thermal lag: heat penetrated the steel envelope rapidly and dissipated slowly, with no thermal buffer to moderate the effect. The GWR container held between 27.8 and 28.6 °C throughout. Energy savings: 41.78%.
The White Control: Why Surface Reflectivity Alone Is Insufficient
The most significant methodological detail of this study is one that is easily overlooked: the uninsulated control container was white.
White paint reflects solar radiation more effectively than uncoated or dark steel, and is widely employed as a passive thermal mitigation measure in tropical and high-solar-load environments. In the context of this test, it represents the most favourable possible starting condition for an uninsulated container. Yet under this best-available passive baseline, the control container exceeded the target internal temperature on every test day - by as much as 5.8 °C - remained outside the comfort band for extended periods, in some cases for more than six hours, and consumed 43% more cooling energy than the GWR NANO INSULATION® container over the four-day period.
This result carries a direct implication for building envelope specification: passive reflectivity-based mitigation is insufficient to maintain thermal control under sustained tropical conditions. Surface reflectivity reduces peak instantaneous heat gain from direct solar radiation but does not provide the thermal resistance necessary to prevent cumulative heat ingress over time.
Air-Conditioning System Load and Service Life
The reduction in cooling system operational load - over 40% across the test period - carries implications beyond energy cost. Air-conditioning compressors degrade faster under sustained high-load operation; shorter, intermittent compressor cycles reduce mechanical wear, extend service life, and reduce long-term maintenance costs. In the GWR NANO INSULATION® container, the compressor operated in short bursts to maintain target conditions. In the uninsulated container, the compressor ran continuously without achieving them.
In any application where the air-conditioning system is sized to maintain comfort under defined thermal load conditions, adding insulation directly reduces annual operating hours and defers the point at which the unit requires servicing or replacement. This represents a capital cost benefit that compounds over the service life of any air-conditioned structure.
Engineering Conclusions
The Vietnam field test is a controlled, instrument-logged demonstration of thermal performance under real tropical operating conditions. The results are consistent with the product’s verified physical parameters - a TÜV SÜD-certified thermal resistance of R = 4.545 m²K/W per 1 mm layer - and extend that laboratory-verified performance into a real-world application under extreme and sustained thermal load.
Three conclusions are directly applicable to building envelope specification:
- At ambient temperatures consistently above 30 °C, uninsulated steel structures cannot maintain internal comfort conditions regardless of surface colour. The question is not whether insulation is required, but which insulation is practical given the spatial, structural and logistical constraints of the application.
- A 1 mm spray-applied nano-coating reduced cooling energy consumption by 43% on average across four test days - without loss of interior space, without structural fixings, and without altering the container’s existing surface geometry.
- The reduction in compressor operating hours directly reduces mechanical wear and extends system service life - a capital cost benefit that accumulates throughout the operating lifetime of any air-conditioned structure.
The test was conducted on standard ISO freight containers, but the underlying physics are substrate-independent. The same thermal resistance properties apply to industrial buildings, warehouses, temporary facilities, roofing systems and any steel or concrete envelope subject to direct solar exposure.
GWR NANO INSULATION® is distributed in Hungary and the Central and Eastern European region by Summotive® (Summa Technologiae Kft.). TÜV SÜD test reports, the Declaration of Performance and technical data sheets are available on request.