Concept illustration of radiative cooling; infrared heat is invisible to the eye.
On a hot afternoon, a roof can feel like the wrong place to find cooling. It sits in direct sunlight, above the very rooms you are trying to keep comfortable.
Yet researchers are developing surfaces that use this exposed position to their advantage. They reflect much of the incoming sunlight while releasing heat in a form that can escape through the atmosphere.
This is passive radiative cooling. The surface itself needs no compressor or electricity to perform the heat exchange. University of Maryland researchers have explained the approach through earlier work on a cooling glass coating: carefully chosen materials can use an infrared “window” in the atmosphere to lose heat towards space. University of Maryland's explanation.
The new question is how to make such materials practical enough for the world outside a laboratory.
A roof has to win two battles at once
First, it must avoid absorbing too much sunlight. Otherwise, the Sun keeps replacing the energy the surface is trying to lose.
Second, it must emit heat effectively. Warm objects give off infrared radiation, a form of light our eyes cannot see. Some infrared wavelengths pass through the atmosphere more readily than others. A suitable surface can use that escape route while remaining exposed to daylight. The cooling-glass research and atmospheric window.
Think of the roof as handling two streams: energy arriving and energy leaving. Its temperature depends on their balance, along with heat exchanged with the surrounding air and building. The intriguing achievement is a surface that can fall below the surrounding air temperature even in sunshine.
The latest example begins with wood
A 2026 Nature Communications study describes a processed, wood-derived biocomposite designed to combine cooling performance with mechanical strength and flexibility. It is an engineered cellulose-based material, not an ordinary plank painted white.
The researchers reported solar reflectance of 94.7%. In an outdoor experiment, the sample reached as much as 8.8°C below the surrounding air temperature during daytime. The material could also be folded or rolled, which makes questions of installation more interesting than they would be for a fragile laboratory sample. The peer-reviewed biocomposite paper.
There is a catch in how that temperature result should be read. The outdoor test used small samples in thermally insulated experimental enclosures. It did not show that a family home became 8.8°C cooler, or that an air-conditioning bill fell by a matching percentage. Experimental details in the paper.
A cooler sample is the beginning of a building story
The gap between those two claims is enormous. A house gains and loses heat through windows, walls, ventilation and occupants as well as its roof. Insulation changes how strongly the roof's temperature affects the rooms below.
That is why a useful building trial would measure indoor comfort and energy use across real weather conditions. It would compare similar buildings or carefully controlled periods, rather than simply photographing a cold-looking patch through a thermal camera.
There is already practical evidence for the broader cool-roof approach. The US Environmental Protection Agency describes reductions in air-conditioning demand and improved indoor comfort from reflective roofs. It also makes clear that outcomes depend on the building and setting. Those findings support the general strategy; they do not certify the new biocomposite's performance on a house. EPA guidance on cool roofs.
The difficult part may be staying useful for years
A roof material must tolerate weather, dirt, maintenance and installation. A strong fresh sample does not establish decades of durability. Nor does a plant-derived ingredient, by itself, tell us the environmental cost of processing and manufacturing the finished product.
Climate also matters. Lawrence Berkeley National Laboratory notes that cool roofs can increase heating needs during cold weather. A building that benefits from shedding heat in summer may want to retain more of it in winter. Berkeley Lab's cool-roof overview.
The promising future is therefore broader than one miraculous coating. Cooling surfaces could become another tool alongside shading, insulation and efficient equipment.
For all the technology involved, the attraction is simple: before spending electricity to remove unwanted heat, make the building better at avoiding it—and better at letting it go.
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