A vast and expensive system with the sole purpose of keeping things cool exists across the developed world. This “cold chain” includes fridges in kitchens, refrigerated lorries and cold store warehouses for supermarket produce and medicines. It costs billions to run and has a big environmental cost. But in poorer countries, this cold chain is just in its infancy. People are dying as health clinics lack the fridges to keep vaccines safe. New cold chain technology is needed and two inventors think they’ve figured it out. World Hacks looks at their innovative ways of keeping things chilled. Presenter: Harriet Noble Reporter: Tom Colls