As with the short-sleeve version, Castelli's Core Mesh Sleeveless Base Layer incorporates an update to the classic fishnet style design. The older design used the holes of what felt like real fishnet to trap air between the skin and the second layer of clothing.

However, with the new fully open mesh design, it still serves to hold the jersey off of the skin, creating a layer of air between your skin and the jersey to help you maintain a constant body temperature. But besides these thermo-regulating properties, the improvements Castelli brings are several. The mesh is made from a polyester hollow core fiber that is soft to the touch, wicks well, and has great stretch. The shape is called "body wrap" because it is designed to wrap or hug the body so that the gaps are only in the mesh, not between the mesh and the body.