India, May 31 -- As mid-day approaches in Bhayander's Navghar area, septuagenarian Sunanda Lakan watches a Marathi television soap with a table fan blowing cool air in her face. In her one-room slum dwelling, she has been keeping the ceiling fan off. "This is enough," she said, pointing to the table fan.

Not too long ago, Lakan's unbearably heated home felt like an oven. But three months ago came a gamechanger-a wood-wool false ceiling attached to the inside of her asbestos roof, which brought the temperature down by five to six degrees.

"There has been some relief after we got this," said Lakan's neighbour Sandeep Sukale, 59, looking up at his own shiny charcoal-grey alu-foil ceiling. His son Prajyot is a Class 12 student gearing up fo...