Out in the sticks of Bangladesh, the threat of flooding means that 70 percent of the population live in corrugated tin huts, most of which aren’t hooked up to an electricity supply. In the heat of the summer, this can practically turn these houses into ovens.

However, a project called Eco-Cooler is spreading knowledge of a cheap and electricity-free method to cool down houses throughout Bangladesh. The beauty of the project is it needs little more than a few plastic bottles and a board. It was started through a collaboration between advertising agency Grey Dhaka and Grameen Intel Social Business Ltd.

Here’s how it works: Plastic bottles are cut in half and then mounted into a grid through bottleneck-sized holes. This grid can then be placed over a window, with the narrower top end of the bottle facing inwards to the house. As wind blows through the bottles, cool air is funneled into the hut. Eco-Cooler say it is possible for this technique to decrease the temperature in the house by up to 5°C – although this figure varies widely based on outdoor conditions.

Not only does it not require any electricity, it also makes good use of disposed plastic bottles. The project has been put online for free, in hopes it can reach as many people as possible. Their initiative has already taken root throughout nearly 25,000 households in villages across Nilphamari, Daulatdia, Paturia, Modonhati, and Khaleya.

“After initial tests, blueprints of the Eco-Cooler were put up online for everyone to download for free," Syed Gousul Alam Shaon, chief creative officer at Grey Dhaka, said in a statement. "Raw materials are easily available, therefore, making Eco-Coolers a cost-effective and environmentally-friendly solution."