I bought an expensive waterproof breathable Jacket a few weeks ago. First ride out i was soaked. Baffled and pissed off i performed a little test of my own. Cupped water with the jacket and let it sit for 10 minutes. Bone dry inside. So obviously i was soaked with sweat. After some searching i find out the "breathable" fabrics can rarely keep up with heavy physical demands, even with pit zip's open.

But i did maintain a comfortable temperature and the wind is also kept out