Remember those string vests they used to sell with the holes in? I had to wear one as a kid sometimes, I was told they were warmer as the holes circulated the air or something, I wasn't convinced, lol!
My mum used to claim that too. She maintained that the string held off the next layer of clothing creating warm air pockets in the holes. I must have been more gullible than you because it was "scientific" enough to convince me.