On October 30, 2026, Germany's Karlsruhe Institute of Technology (KIT) highlighted research trends in "caloric cooling," which uses temperature changes in solid materials. The announcement followed the publication of a peer-reviewed review by Kun Wang and colleagues in the journal Nature Energy on the same day. It does not announce the development of a new cooling device. The review compares the four main caloric cooling approaches across a wide range of factors, from material properties to overall device performance.
Caloric cooling moves heat using the temperature change that occurs when a stimulus, such as a force or a magnetic field, is applied to a solid material. Earlier studies have produced prototypes with cooling capacities above 1 kW. However, a large temperature change in a material is a separate matter from whether a device can cool efficiently with little energy. In fact, the 1,284 W cooling capacity recorded by a previous device was measured with zero temperature difference between the cold and hot sides.
Four types of stimuli make solid materials carry heat
In caloric cooling, an external stimulus changes the temperature of a solid material, and cooling is achieved by repeatedly absorbing and releasing heat. The material takes up heat from the object to be cooled and releases it elsewhere. The technology falls into four main approaches, depending on the stimulus used.
| Approach | Stimulus applied to the material |
|---|---|
| Magnetocaloric | Magnetic field |
| Elastocaloric | Mechanical force such as tension or compression |
| Electrocaloric | Electric field |
| Barocaloric | Pressure |
Because the devices that generate each stimulus and the shapes of the materials differ, it is difficult to judge the merits of an entire cooling system from the material's properties alone. Caloric cooling could eliminate the need for conventional refrigerants, which have a large global-warming impact. At the same time, the mechanisms that apply stimuli to the material and the equipment that moves heat both require energy.
In their review, Wang and colleagues also include conventional vapor-compression cooling and thermoelectric cooling as points of comparison. They examine energy efficiency, temperature difference, and cooling power density, as well as durability and cost. As examples of materials research progress, they cover shape-memory alloys that resist fatigue from repeated deformation, electrocaloric elements with multilayer structures, and elastocaloric systems using natural rubber. However, this is a review that organizes existing research results, not a new experiment comparing the four approaches under unified conditions.
The test conditions behind the 1,284 W cooling capacity
According to KIT, prototypes using magnetic fields have reported cooling capacities above 3 kW, and devices exceeding 1 kW have also been developed using mechanical force. These figures all represent cooling capacity, meaning the amount of heat that can be moved per unit time. They do not indicate power consumption or energy efficiency. Nor were they measured under standardized test conditions, so the approaches cannot be ranked simply by comparing the numbers.
One of the earlier studies cited in the review is the 2025 peer-reviewed Nature paper by Guoan Zhou and colleagues, "Achieving kilowatt-scale elastocaloric cooling by a multi-cell architecture." According to the published abstract of the original paper, the research team built a device that combines multiple cooling cells, using thin-walled nickel-titanium alloy (NiTi) tubes whose temperature changes when compressed. The cells are arranged mechanically in series, while the fluid that carries heat flows through them in parallel. Heat exchange used a fluid containing graphene.
The 1,284 W recorded by this device is the fluid-side cooling capacity measured over the first 500,000 cycles at an operating frequency of 3.5 Hz, with zero temperature difference between the cold and hot sides. It is an experimental value obtained from the actual device, not a result of the fluid simulations included as supplementary material in the paper. However, it does not show cooling capacity or energy consumption with a temperature difference present, so the value alone cannot be used to judge efficiency in real air-conditioning applications. Also, 500,000 cycles refers to the number of repeated operations and is different from the number of prototypes or independent trials. These numbers cannot be confirmed from the published abstract.
It is particularly important not to confuse the maximum cooling capacity obtained at zero temperature difference with real air-conditioning performance. Keeping a room cooler than the outdoors requires continuously moving heat against a temperature difference. Recording 1,284 W at zero temperature difference does not mean the same cooling capacity would be obtained in an environment with an indoor-outdoor temperature gap.
A material's temperature change alone cannot gauge a cooling device's efficiency
Evaluating a cooling device requires distinguishing cooling capacity from energy efficiency. Cooling capacity is the amount of heat that can be removed per unit time, whereas the coefficient of performance (COP) is the heat removed divided by the energy input. A device with a large cooling capacity does not necessarily have a high COP if it needs a great deal of energy to run. Moreover, unless the temperature difference between the cold and hot sides during measurement is matched, it is hard to compare performance under conditions that reflect real use.
Cooling capacity converted to a per-mass basis for the material also calls for caution. Zhou and colleagues report cooling capacity per unit mass of material, but a real device needs not only the cooling material but also components such as drive mechanisms and heat exchangers. A per-mass figure for the material alone therefore cannot be treated as the cooling capacity per mass or volume of the entire device.
KIT names heat loss, material fatigue, and the inability to fully recover the mechanical or electrical work put in during the cooling cycle as the main reasons the properties of a material and the performance of a finished cooling device diverge. These are explained as factors that affect device performance, however, not as the results of measuring how many percent each one reduces performance. Judging the practicality of caloric cooling requires evaluating not only how large a temperature change a material produces, but also how fast heat can be transferred, how much energy is needed to drive the system, and what energy-recovery mechanisms are in place.
Durability and performance under real operating conditions are key to practical use
KIT explains that using caloric cooling over the long term requires materials that can withstand millions of repeated operations, absorb and release heat quickly, and be driven with little energy. Material fatigue from repeated loading is a particularly important issue for approaches that rely on mechanical deformation. However, the figure of millions of cycles is a benchmark of the durability needed for long-term use, and does not mean every prototype has reached that level.
Jingyuan Xu, the review's corresponding author, points to applications where conventional cooling technologies face practical constraints as the areas where caloric cooling may first spread. Specifically, these could include environments that require quiet operation and uses where people want to avoid refrigerants with a large global-warming impact. Still, showing potential in such applications is distinct from demonstrating that the technology can fully replace existing cooling systems.
Although the review has been peer reviewed, that does not mean that every device performance figure it cites has been independently replicated. The published abstract does not make it possible to confirm the total number of studies the review covers, the detailed selection criteria, or whether independent replications under identical conditions have been carried out for earlier devices. The performance values obtained in individual studies therefore cannot be generalized directly to different materials, devices, or applications.
In judging future practical use, the key question is how much heat can be moved while maintaining the temperature difference an actual application requires. That evaluation must also consider not just cooling capacity but the energy input of the entire device, including its drive mechanism, and how well performance holds up after long periods of repeated operation. As data of this kind accumulate under standardized test conditions and in demonstration units close to real applications, the basis will be in place for assessing whether the potential shown in materials research can become a practical cooling technology.