MIT built a three-layer passive cooling panel of aerogel, hydrogel and reflective material; tests cooled it 9.3°C below ambient and suggested up to 40% longer food storage in humid conditions

On extremely hot days, the typical modern response is almost instinctive: lower the room thermostat, take out a cold beverage from the refrigerator, and reach for the ice maker; in short, allow another machine to handle the heat. Yet, there is a drawback inherent in such an approach to dealing with extreme heat conditions, and that is the fact that cooling requires energy. As the temperature rises higher, demand for air conditioning and refrigeration also increases. This eventually puts additional strain on power sources and makes reliable cooling harder to access in places that lack electricity.

According to a 2022 MIT News article, researchers at MIT created a passive cooling system that uses evaporation, radiation and insulation instead of electrical power. At first glance, the concept looks simple, with a three-layer composite that consists of aerogel, water-saturated hydrogel, and reflective insulation material. The manufacturing behind it, as it turns out, is not as simple. During tests in a rooftop location, the small-scale model of this cooling mechanism managed to cool down to almost 9.3°C (19°F) below the ambient air. Under particularly humid environments, the researchers calculated the new system can extend the shelf life of perishable foods by almost 40%, while lower humidity increased the potential much more.

What's actually inside this thing


This design consists of three layers stacked one above another, and all of them have their individual roles. Aerogel is placed at the top. It is an almost weightless material resembling a sponge, basically made of trapped air. The aerogel layer allows water vapor and infrared radiation to move upward while protecting anything beneath it from external thermal energy. Beneath it lies a layer of hydrogel that resembles a wound dressing or a cooling pad. It slowly emits water vapor upwards, where it passes through the aerogel layer and evaporates, thus taking the heat with it. And finally, there is the bottom layer resembling a mirror reflecting the sunlight directly back without heating the entire panel.

Combining all three efforts produces a device that is colder than the surrounding air through the principles of physics alone. As stated in a research paper titled “Significantly enhanced sub-ambient passive cooling enabled by evaporation, radiation, and insulation,” published in the journal Cell Reports Physical Science by the MIT team in September 2022, the panel increased the time of safe food storage by 40% in extremely humid environments and had the potential to triple it in less humid surroundings. The only maintenance the device requires is replenishing the water needed for evaporation, which should be done once every four days in arid environments and once a month in more humid ones.

This isn't a contradiction between the two figures above; it's actually consistent with them. Evaporation happens more slowly when the surrounding air is already moisture-saturated, which is exactly why the hydrogel loses water more slowly (and needs refilling less often) in humid climates. That same slower evaporation is also why the storage-life boost tops out at 40% in humid conditions rather than reaching the tripling seen in drier climates, where faster evaporation drives more of the cooling.

Why this actually matters

The timing is very essential. As reported by the International Energy Agency, space cooling has become the fastest-growing area of energy demand from buildings all around the world, while in the U.S., air conditioning already takes up a significant amount of the energy required during summer peak usage hours, precisely the sort of scenario that leads to rolling blackouts and grid failure in hot weather conditions.

The UN's Food and Agriculture Organization has reported that insufficient refrigeration contributes to the loss of about 526 million tons of food each year. A panel device such as the aforementioned will not solve the problem of grocery store supply chain logistics immediately in America, and it isn't a near-term option for commercially regulated settings like food trucks or farmers' markets either, since those operate under health codes that require active, powered refrigeration. Where it could plausibly fit sooner is remote cabins, farmers’ markets, food trucks, emergency relief packs, and an increasing number of youngsters trying out the van-dwelling and homesteading lifestyle, this can be a viable option that does not yet exist on the shelves.

The quiet part you may have ignored

The hard truth about this is that you can’t buy it right now, and there’s no specific date of its release either. What makes the biggest difference is that the aerogel layer still costs a lot to produce, as it needs a special procedure for drying. As mentioned above, this is where the "simple concept" runs into a genuinely hard manufacturing problem. The MIT scientists, including postdoc Zhengmao Lu and professors Jeffrey Grossman and Evelyn Wang, have stated that the main problem is not physics but the possibility of scaling up production.

Thus, before buying from anyone who sells "off-grid AC panels", keep in mind that it is just a prototype for now. The science works, but the logistics of bringing this to your roof is yet to be figured out. Nevertheless, in a world where "power is not needed" can almost sound revolutionary, it is definitely something to watch out for.