Charcoal blanket



*** PILOT COOLERS available for testing ***

In case you would like to help us test and optimize this charcoal cooling blanket, please contact . Upon availability, we could send you a charcoal blanket cooler room (1.5 x 1 x 0.4 m) with a capacity of 600L, as is shown in the movie, or a smaller 56L cooler for a single box of fruit. We can help you (virtually) to setup and install it and also provide sensors so you can monitor the hygrothermal behavior inside and outside the cooler. Note that we prioritize research institutes and startups that are located in developing countries. We can provide you with such a free testing kit. What we would expect in return is a few nice pictures, sensor data of the cooler during operation and a short user story on your experiences.

Type. Empa Internal

Funding. Empa innovation booster

Duration. 2021-2023

Collaborations. BASE

Staff. and Daniel Onwude

Project background

Evaporative cooling is a high-potential technology to help preserve fresh produce after harvest. This passive cooling solution is especially interesting for marginal and smallholder farmers in remote, off-grid areas. However, evaporative coolers are still rarely deployed. We currently lack simple, small-scale evaporative cooling systems that are affordable for marginal and smallholder farmers. As a solution, we present, design, and test an alternative evaporative cooler – a charcoal cooling blanket. The blanket can be made in any size from locally-sourced materials such as charcoal and burlap or other biodegradable textiles. The blanket's cost scales down quasilinearly with the length of the blanket. The blanket has several compartments and is semi-self-supporting. When building a cold storage room or retrofitting sheds to cooling rooms, the blanket acts as a structural component. The blanket is useable throughout the supply chain. This charcoal blanket lowers the expertise to construct and operate evaporative coolers. It reduces the cost of microscale cooling facilities. With these features, we aim to catalyze the deployment of evaporative coolers. We also present a business solution to accelerate the adoption of this technology.

Flowchart on how to construct a plug-and-play charcoal cooler. Step [1]: filling a crate with fruits and placing temperature and humidity sensors on the fruits; [2] filling the sewed burlap blanket with charcoal; [3] mounting wooden poles at the farm; [4] wrapping the charcoal blanket around the mounted poles; [5] covering the cooler with tarps and watering the charcoal blankets; [6] placing the filled crate of apples in the charcoal cooler for preservation.


Defraeye T., Schudel S., Shrivastava C., Motmans T., Umani K., Crenna E., Shoji K., Onwude D. (2022), The charcoal cooling blanket: A scalable, simple, self-supporting evaporative cooling device for preserving fresh foods, Preprint DOI.

Defraeye T., Shoji K., Schudel S., Onwude D., Shrivastava C. (2022), Evaporative coolers for postharvest storage: where to best use them and how well do they work? ,Preprint DOI, Cooling Map, and the Repository.