The Base Top is super lightweight, has great ventilation, and dries very quickly. When you wear the top on the warmest days, it will have a cooling effect against strong heat. The sweat dries quickly and your core temperature will continue to be stable. It is also perfect for use under your cycling jersey on cold days as an insulating layer. The top has a very tight fit and is designed to sit as closely as possible on the body. We recommend going up a size if you are in doubt, or if your body measurements fall between two sizes.