# City University of Hong Kong develops a cooling layer reducing temperature by 5.2°C

- Published: 2026-11-08 15:51 UTC
- Section: Machines & Making › Materials science
- Tags: cooling coating, porous plastic, temperature reduction, energy efficiency, City University of Hong Kong
- URL: https://realtech.media/news/rt-2109aa95dd72a002aa9e9228_city_university_of/

**Researchers created a lightweight porous plastic layer that enhances outdoor cooling coatings, potentially reducing energy demand for air conditioning.**

![City University of Hong Kong develops a cooling layer reducing temperature by 5.2°C](https://realtech.media/media/2026/11/b80123a15cc4a7a0.jpg)
*Hardcoreraveman, Wikimedia Commons, Public domain*

Researchers at City University of Hong Kong have developed a lightweight layer of porous plastic that helps outdoor cooling coatings achieve a temperature reduction of up to 5.2 degrees Celsius compared to coatings without the layer. This innovative material allows heat to escape while blocking much of the sunlight that would otherwise warm the surface, making it a promising solution for reducing energy consumption in buildings.

The layer is designed to improve coatings that cool without electricity. If successful at building scale, it could significantly aid in heat shedding from roofs during the day, thereby decreasing the demand for air conditioning. These coatings function by reflecting sunlight and emitting heat as infrared radiation. Certain infrared wavelengths can penetrate the atmosphere and escape into space, enabling surfaces to cool below the ambient air temperature.

In their study, published in Energy & Environmental Science, the researchers created a white aerogel from a type of polyethylene with long molecular chains. The aerogel's structure features numerous small pores, allowing it to serve as an insulating layer while permitting specific infrared wavelengths to pass through. The material demonstrated an impressive ability to reflect up to 96.6% of incoming sunlight and transmit up to 94.5% of targeted infrared light, effectively protecting the surface while facilitating heat dissipation.

The team conducted outdoor tests in Hong Kong and Abu Dhabi, where the largest temperature drop recorded in Hong Kong was 5.2 degrees Celsius. In Abu Dhabi, the covered sample maintained a cooler temperature than the uncovered coating during extended outdoor testing. Additionally, the researchers modeled energy use for a four-story apartment building, estimating that the layer could increase energy savings from a cooling roof by approximately 55% in the Abu Dhabi scenario.

An accelerated test exposed a sample to ultraviolet light for 75 days, revealing minimal changes in its ability to reflect sunlight and transmit relevant infrared wavelengths, suggesting durability against prolonged sun exposure. While the outdoor tests provided valuable data, full roofs would raise further questions regarding installation and long-term performance under various weather conditions. This work offers designers a method to separate the dual functions of a single coating, allowing one layer to protect against incoming heat while the underlying coating continues to release it.

## Sources

1. [knowridge.com](https://knowridge.com/2026/11/a-lightweight-layer-helped-roof-coatings-stay-cooler-in-direct-sunlight)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-2109aa95dd72a002aa9e9228_city_university_of/