A passive radiative cooling film kept a coated 20-foot container below 34.2°C in peak Mediterranean summer conditions while an identical untreated box next to it hit 53°C — with zero energy consumption. Those are the headline results of a pilot run last summer by startup Cooling Photonics at the Transbase Soler depot in Valencia, now formally presented through the Valenciaport Sandbox, the Spanish port's live testing ground for port and logistics technology.

The numbers matter for anyone shipping heat-sensitive cargo through southern Europe. Over fifteen consecutive days, four identical 20-foot containers with the same solar exposure were monitored. Independent sensors recorded internal temperatures every 15 minutes, producing more than 5,600 readings.

What did the test measure?

The four boxes were configured as follows:

• One untreated reference container
• One fitted with a conventional internal thermal blanket
• One with the cooling film applied to the roof only
• One with the film on both roof and side walls

The verdict was unambiguous. The standard container spent more than a third of the monitoring period above 40°C. The fully coated container never breached 34.2°C. Daily peak temperatures fell by an average of 17.5°C, with a gap of up to 22°C on the hottest day of the trial.

The material, CoolPly, works differently from insulation. Rather than trapping heat inside the steel shell, it reflects solar radiation before it penetrates the box and allows the container to cool naturally at night.

Why does this matter for operators?

For depots, terminals, logistics operators and carriers, the commercial implications are direct. Cargo and equipment stay below 35°C without any power draw, limiting heat peaks and reducing thermal stress and material fatigue. That translates into fewer claims risk on temperature-sensitive goods stored in static containers and less equipment degradation.

The applications extend beyond boxes sitting in depots. Containers used as warehouses, workshops or site offices become safer workspaces, cutting heat stress for staff. Electrical cabinets and powered port equipment benefit too — lower internal temperatures mean fewer shutdowns and longer life for power electronics. And as summers intensify across Mediterranean trade lanes, the film functions as a climate adaptation tool, a resilience play rather than just a cost play.

Who backed the trial?

The pilot ran through the Valenciaport Sandbox with support from Opentop, Valenciaport's open innovation hub, which connected the startup with a real operational environment. Fundación Valenciaport coordinated the port community collaboration.

Juan Manuel Díez, Head of Innovation at the Port Authority of Valencia, said the Sandbox was built so that innovative ideas can prove their value in real port operations, with data gathered on the ground. "This pilot is a great example: a technology tested in our port that delivers practical, measurable results and can help the entire sector become more efficient and sustainable," he said.

Salvador Furió, Deputy Director General and Director of Innovation and Development of the Cluster of Fundación Valenciaport, said the pilot shows the Fundación's commitment to startups and scaleups. "Through Opentop, we facilitate their access to the Port Community so that they can validate their solutions in a real environment," he said.

Host operator Transbase Soler saw the results first-hand. Alfredo Soler, CEO of Transbase Soler, said: "Seeing a container go from 50 degrees to just over 30 without using any energy is something that interests us all."

Javier Achiaga, CEO of Cooling Photonics, called the depot trial in high summer "the best possible validation" for CoolPly. "The results show that the port and logistics sector has a real opportunity ahead: protecting cargo, improving working conditions and reducing energy consumption with a passive solution," he said, adding that the company will continue developing new materials.

With the pilot data now published, the question for shippers and depot operators is scaling: a passive film that removes nearly 18°C from peak interior temperatures, with no reefer fuel and no plug, positions itself as a low-cost complement to active reefer capacity as Mediterranean summers grow hotter.