I have two of these, but have yet to use either in vest mode. I absolutely love them. Hard to figure out how something so thin and comfortable can work so well, but it does. 50-60 degrees F, I wear a compression underlayer, a short sleeve jersey, and this jacket. I' m never cold or hot. Perfect. No wind gets through, and on sunny days, it seems to radiate heat. On days colder than 50, I prefer high end Gore wear. Gore makes some fantastic stuff, but it's not cheap. The PI can be bought at great prices on Amazon.