The Castelli Core Mesh Short Sleeve base layer is the perfect minimalist piece to keep you cool in warm weather. The fully open mesh serves mainly to hold the jersey off the skin, creating a layer of air between your skin and the jersey to help you maintain a constant body temperature.
A body wrap design with an unbelievable amount of stretch makes for a great fit. The fabric absorbs practically no moisture, and it weighs next to nothing so it won't weigh you down. Widely considered to be one of the best base layers in cycling.