by Son of a Beach » Fri 11 Nov, 2011 8:28 am
I was looking for waterproofness in the poll first too, but your explanation does make sense. There are actually some rain jackets that a really not waterproof though - at all. Thankfully, I've never owned one of those.
I have experienced good breathability in a rain jacket, and I was so impressed that I had to select it as my top priority. My jacket has spent the entire night sitting in a puddle, and then hidden under slushy snow. During the walk out, in the rain, I wore it all the way, and it was completely dry inside within about 2 hours. I think it was the very cold air outside that helped. It made me realise how much difference the right weather conditions can make to a jacket's breathability, as I've never found the breathability to be that good before or since. If only they could make fabrics that work that well all the time, I'd be a very happy camper.
Yes, of course opening the front zip will provide better ventilation/breathability than the fabric itself, but taking off the jacket completely would be even better still. However, neither are appropriate in some weather conditions, and both could result in you becoming wetter, despite the better breathability. After all, with a rain jacket, its primary purpose is to minimise how wet you get.