During rides that involve low temperatures, your base layer acts as an insulator for your body. Similarly, in warm weather, that same layer under your jersey works to pull moisture away from your skin in order to keep you cool and comfortable. Castelli understands that the inconspicuous under-layer is hard at work regardless of your riding weather, which is why it introduced the Seamless Base Layer.
Castelli's Seamless Base Layer was constructed using two fabrics: polypropylene and nylon. These materials work in tandem in oder to perform the base layer's primary function -- pulling moisture away from the skin and drying it. Accordingly, the inner-layer is comprised of the polypropylene material, as it effectively pulls moisture away from the skin and transfers it to the outer-layer of nylon. And because nylon is lightweight and maintains an airy composition, it's a naturally efficient evaporator. The material dries much quicker than most, which means that instead of simply soaking you in your sweat, the base layer keeps you cooler by evaporating moisture next to the skin.
This moisture transfer is furthered by the three different mesh patterns on the base layer. Taking anatomy into account, this system maintains a consistently open mesh in order to provide the most ventilation possible, which keeps your body dry and comfortable throughout your rides.
The Castelli Seamless Base Layer is available in the sizes Small/medium, Large/x-large, and XX-Large and in the color White.
This base layer did exactly what I was hoping it would do. It helps me maintain an even body temperature in various Fall climates and keeps my jersey from getting sweaty and cold against my skin. It works well for me in temps from mid 50 degrees to mid 80 degrees, but I have hopes that I can use this base layer year round. Very impressed with the quality as well. I can barely tell it's on when I wear it. One note, when you get first pull it out of the box it will be tiny like a child's shirt. I'm 5'10' 150lbs. and the S/M fits perfect.
The large seem small but stretches for a nice fit. it is very comfortable and warm but not hot. The mesh is like magic and keeps me dry.