I was skeptical about using a material like the one on this jersey, but it's been as advertised. Perfect for:
Mornings where it's 50 degrees but will heat up to 65 when you're done
Windy days where expected on and off showers are going to happen

The best cocktail for this is to wear some decently thick arm warmers, sleeveless baselayer, and bib shorts. I've used it under a jacket during a 40 degree day and it worked great, but this jersey really fills a niche when it's not covered. Replaces the need for a vest on most days you would wear one.

RE: fit, it does run European sizing as Gore seems to do. It's one of only 2 jerseys I have that are larges, including my Giro SS Jersey. The sleeves were a bit long for me but I like the fit since they're tight. It has a high neck collar, which I've never seen on a jersey, and rides up a bit in the back, but looks cool and keeps your neck warm and/or protected from the sun.

All in all, extremely happy with this purchase, that I hope will last 8-10 years.

I love when a company reads my mind. I struggle with staying warm on the road bike when I ride in the mornings around the mountains. Leaving the house, it is full jacket weather, first climb, sweat and overheating, then first descent, freeze, repeat. My current solution is clunky, I wear a wind proof baselayer, jersey, jacket. but then I end up sweating through the base layer and getting a chill on the descent. So I go this and BOOM, fix the problems. I can wear a nice baselayer under and this on top, maybe some arm warmers, and I am good to go for my morning rides. Sweat doesn't build up since the material moves moisture and blocks wind. It keeps you warm on the descent and the flats, without over heating, and up the climbs, open up the full zip and you have perfect venting. The fit is trim, so I went to a large, I normally wear medium in most american cycling brands, large in Castelli, medium in most Assos. The sleeves are lang and good for keeping that style fresh, but not so long they are intrusive. The cut allows for nice articulation when you are riding in the drops. And the material is not "waterproof" because it doesn't have taped seams... whatever, it takes a massive downpour for you to get wet, the Gore Infinum is HIGHLY water resistant. I have the Infinum XC ski jacket too, it is the best material I have ever used for cold aerobic activity.