Bangladeshi inventor Ashis Paul has figured out how to repurpose plastic bottles into a low-cost, easy-to-make, electricity-free air conditioner that can help the country's poorest better tolerate the sweltering summer heat.

The science behind the Eco-Cooler is based on the idea that the bottleneck becomes a funnel that compresses and cools the air that runs through it by about five degrees, according to the Eco-Cooler website. It's the same principle that governs blowing air through pursed lips — the air comes out cooler despite the body's 98-degree-Fahrenheit temperature.

Volunteers install eco-coolers.

The AC unit also adds to the list of ways plastic bottles can be recycled. Around 50 billion water bottles are used on an annual basis, and only 20% get recycled — the rest end up in landfills.

In the summer, temperatures in Bangladesh, where many rural citizens live in tin huts and without electricity, can reach up to 113 degrees Fahrenheit. These eco-coolers would act as a window in the walls to catch passing breezes.

Over 25,000 eco-coolers have been installed in Bangladesh so far by Grameen Intel employees and Grey Dhaka volunteers.

The DIY air conditioner has no copyright, and an instruction manual for making one can be found online, encouraging anyone interested to build one.