The Sottile Due (say: so-teal'-ay do-ay) Jacket is Castelli's vision of a thin and extremely light and packable weather barrier. The jacket is somewhat breathable, but its real focus is protection that comes in a tiny profile. Think of it as a lightweight storm jacket or a modern day rain cape that is more packable, actually breathes and works well in windy conditions.
The thin and low volume composition of the Sottile make it the ultimate storm jacket due to its storage capacity. Take it along on days you are unsure of the weather or climbing up to altitude and it might get chilly on the way down. It offers a ton of security and compresses down to the size of an energy bar and weighs in at under 100 grams. The Sottile is anatomically correct and made to fit the body while in the cycling position. This type of tailored fit drastically cuts down on wind flap which can plague this type of jacket design. Ends of arms and body are hemmed and cuffed. The neck area has perforations as does the under arms for some added ventilation. The rear of the jacket has a vertical zipper for under-jacket access.
Bought this last week as a packable emergency rain shell for use on warm rides (replacing classic PVC rain cape), and it met the mark today on a 70F ride with a cold front approaching. I tried using it early-on during some sprinkles, but found it way too hot for even a mile (65-70F, worn over a jersey and summer base layer shirt), and put it back in my pocket. The front hit ~3hrs later, dropping the temp from 70 to the mid 50's and pitting me against rain/hail and a 30mph headwind for the final 5 miles. The superlight jacket covered this stretch as advertised, blocking the wind and keeping the chill at bay to get me home. While no wind and only a little water penetrated, the ultralight fabric did cling to me and feel a bit clammy. It packs very, very small, as advertised, taking about 1/2 of a jersey pocket.
Pros: Packable, windproof, water resistant
Cons: Limited breathability, much more $ than rain cape