Miracle bioplastic cools buildings without power

New biodegradable cooling film slashes energy use up to 20%

Imagine wrapping a building in a layer of material thinner than a sheet of plastic, and watching its internal temperature drop by nearly 10 degrees in the middle of the day, under direct sunlight, with no electricity, no refrigerant, and no machinery: that is precisely what a new bioplastic metafilm developed by researchers at Zhengzhou University and the University of South Australia (UniSA) is designed to do.

Recently published in *Cell Reports Physical Science*, the study describes a structural film made from polylactic acid (PLA) – a biodegradable plastic derived from plant sources such as corn and sugarcane. Through a low-temperature phase separation technique, the material develops a porous, bi-continuous microstructure that gives it two exceptional properties: it reflects 98.7% of incoming solar radiation, and it emits heat directly into outer space through the atmospheric window — the narrow band of infrared wavelengths that pass through Earth’s atmosphere unimpeded. The result is passive radiative cooling: the building surface becomes colder than the surrounding air, even at noon on a clear day.

The numbers behind the breakthrough

The performance data published in the study are striking. In field tests conducted in both China and Australia, the metafilm produced an average temperature reduction of 4.9°C during the day and 5.1°C at night. Under peak solar intensity (around 945 W/m²), it achieved a maximum sub-ambient cooling of 9.2°C, with an average cooling power of 136 W per square metre – comparable to a small electric heater running in reverse. Computational simulations showed that applying the film to buildings in cities like Lhasa, China, could slash annual energy consumption by up to 20.3%, primarily by reducing reliance on air conditioning. That figure matters enormously: according to the International Energy Agency (IEA), air conditioning and electric fans already account for roughly 20% of total electricity used in buildings worldwide, the equivalent to 10% of all global electricity consumption. Demand is only growing: the IEA projects the global stock of air conditioners will reach 5.6 billion units by 2050, up from around 1.8 billion today, tripling energy demand for cooling in the process. A Nature Communications study published in 2024 estimated that residential cooling electricity consumption alone could nearly double by mid-century, reaching up to 2,377 terawatt-hours per year and emitting over 1,300 million tonnes of CO₂ equivalent annually. Against that backdrop, a passive, zero-energy cooling material that also degrades naturally at end of life is not merely a scientific novelty — it is a potential cornerstone of climate strategy.

What’s different this time

Passive radiative cooling is not a new idea: the science has been understood for decades, and several materials capable of the effect have been developed (we also wrote about some of these attempts. The obstacle has always been durability and sustainability: mMost existing passive cooling systems rely on petrochemical-based polymers or ceramics – materials that work well but carry a significant environmental cost in production and disposal. Bio-derived alternatives have historically failed under real-world conditions: prolonged ultraviolet exposure degrades their structure, and contact with acidic rain or pollution erodes their cooling power.The PLA metafilm solves both problems: after 120 hours of immersion in strong acid (pH 1) and the equivalent of eight months of outdoor UV exposure, the material retained a cooling effect of 5°C to 6.5°C, a result the researchers describe as demonstrating “durable” outdoor performance. Its thermal conductivity is also exceptionally low at 0.049 W/m·K, minimising heat transfer through the film itself. Critically, PLA is already produced at industrial scale worldwide, primarily for packaging and medical applications. This means the manufacturing infrastructure for scale-up already exists, lowering the barrier to commercialisation.

Beyond buildings

The researchers emphasise that this film is not limited to building facades and rooftops. The same properties that cool a concrete wall under a summer sun could be applied across a wide range of sectors. The team is currently exploring applications in transportation (cooling vehicle surfaces), agriculture (protecting crops and livestock from heat stress), electronics (passive thermal management of devices), and even biomedical uses such as cooling wound dressings. Cities are warming faster than rural areas, a phenomenon known as the urban heat island effect, which the IEA estimates can increase air conditioning energy consumption by an additional 20% in dense urban environments. Traditional building materials – concrete, asphalt, dark roofing – absorb solar energy and re-radiate it as heat, raising ambient temperatures and creating a feedback loop: hotter cities demand more cooling, which requires more electricity, which produces more emissions, which warms the climate further. A passive film that reflects nearly all incoming solar radiation and radiates heat directly to space breaks this loop at its source. Applied at urban scale, it could contribute not only to individual building efficiency but to measurable reductions in city-wide temperature profiles. The team is now pursuing large-scale manufacturing partnerships. Unlike many laboratory breakthroughs that remain confined to controlled conditions, this metafilm has already been validated outdoors under harsh environmental conditions across two continents. The fundamental material, PLA, is readily available and cost-competitive. The fabrication technique, while specialised, is described as scalable. The cooling crisis is accelerating, and surely the this bioplastic metafilm will not solve it alone, but as a zero-energy, biodegradable, scalable material that cools passively and performs under real-world conditions, it offers something rare in climate technology: a solution with no obvious trade-off between performance and sustainability.