Following the suggestion made by OCR, I tried out a Hyperkewl evaporative cooling vest on today’s 90 something degree (F) ride. I’d say it was a success. It wasn’t the same cooling as getting out of the sun or having a 20 degree temperature drop, but it definitely helped. The vest was very comfortable. Other than the cool feel, I couldn’t really tell I had a vest on under my mesh jacket.
I wish I had bought one of these long ago.