The Castelli Idro has the weight and bulk of a light wind layer, but the breathability and water resistance of a 3-layer hardshell. Not only that, after months of use rain still beads off the jacket the same it did when it was brand new. I stay warm and comfortable for hours in the rain. This is a must-have for anyone who is doing a lot of riding in the rain.
Being 5'7 and 140 pounds, I went with the large and it fits pretty much perfect. I tried the Goretex Shakedry and regardless of size, it just was either way too big or way too small. The Castelli is a little tight around the shoulders but in the drop position, it is fine. It does repel the rain very good without overheating, and it fit's perfect in the back pocket for those days it may or may not rain. All in all, definitely size up but i think you will be happy
The Idro jacket is my outer layer for my ultra-race kit. Super light. Fantastic rain and wind block. Packs down to almost nothing. Every ounce and cubic inch counts but mostly things have to work. Normally wear an XL in Castelli tops but went with the XXL so I have a little more space for layering when it gets cold.
The Castelli Idro is one of a handful of jackets that use the Gore-Tex Active membrane. The Gore-Tex Active membrane works really, really well. Rain beads off and after a month of use, there's no change in how well water rolls off. I stayed totally dry from inside and out and very comfortable on a 2 hour ride in low 40's with steady rain. I've done a few shorter rights in higher temperatures and intensity and notice the breathability is comparable to a wind jacket. The Idro is very compact, easily folding small enough to fit in a standard jersey pocket.
The main difference between the options that use the same Gore Active material is the cut and fit of the jackets. The Idro fits snug body, with high arms, slim sleeves, and tight cuffs. I'm relatively slim for my weight and the fit works great for me. Castelli uses a large, chunky zipper that is easier to use while riding and with gloves on.
The Idro is expensive, but it has the refined fit and performance to justify the price for me.