At the big NeoShell launch in Boston last November, Polartec gave me a Westcomb jacket made out of their new waterproof breathable fabric. I have put the hardshell jacket through the paces, wearing it for hiking through downpours in San Francisco and ice climbing in Ouray, Colorado.
As you recall, NeoShell differs from other waterproof breathable fabrics in that it allows a tiny amount of air permeability. This air permeability is imperceptible from a wind chill standpoint but helps to significantly accelerate moisture vapor transport out of the jacket.
During my wet weather hikes, the NeoShell jacket kept me perfectly dry. With only a thin wool base layer underneath, I could actually tell their was more air flow throughout my jacket but not enough that it felt like the wind was cutting through.
The nice thing about NeoShell is that you don't have to get all hot and sweaty first before the jacket actually starts to remove the moisture vapor. Even before I was really moving hard on my hikes, I could feel my initial sweat being wicked away.
Where the NeoShell jacket really shined for me was in ice climbing. For most climbs outside of the Ouray Ice Park, I needed to wear a hardshell jacket, as it was either snowing or part of the ice was wet, and it was almost always windy.
In multi-pitch ice climbing, periods of strenuous climbing activity are followed by periods of standing in one place while you belay the lead climber. It is imperative that you are not sweaty at the end of climbing your pitch or you will freeze once you stop moving.
I climbed all day in my NeoShell jacket and was always dry from both inside and out. One other small detail I like about the waterproof breathable fabric is that it feels softer and doesn't "crinkle" like a traditional hardshell jacket. It almost feels like a waterproof softshell.
Bottom Line: I can't tell you exactly how much more air permeability NeoShell has over a typical waterproof breathable jacket, but from my experience, it was perfect at keeping the rain, snow and wind completely out while letting me participate in active, cold weather, outdoor pursuits such as hiking and ice climbing without getting sweaty-something that was crucial to me staying warm all day. Polartec NeoShell makes the perfect hardshell material for more active outdoor sports where you need to block wind and stay dry both inside and out.