It's mostly made of mesh to ensure sufficient ventilation, and the ankle is especially stretchy to ensure full pedal-friendly comfort. Castelli made it out of Meryl Skinlife yarns for ultralight thermal regulation suitable for warmer weather. 200-needle construction for extra stretch Lightest mesh ankle and top of foot for hot-weather comfort Midfoot support band Meryl Skinlife yarns with antimicrobial silver ions to reduce odor