New Delhi, Sept. 5 -- Dear reader,

On a sultry July morning this summer, I spent some time with food delivery workers at a cafe in South Delhi. We discussed the hazards they face, such as a lack of drinking water and toilet facilities or the occasional climbing of stairs to deliver an order. The purpose of the meeting was different. I was keen to understand if wearing a 'cooling vest' made their lives any better during the punishing summer months.

This summer, over 7,000 cooling vests were distributed to people who work outdoors, literally with their feet-on-the-street, such as gig workers and construction labourers. The jackets have a layer of polyvinyl alcohol (PVA), which can absorb water and slowly release it as vapour, cooling vita...