The key behind a top-notch base layer is to keep moisture off your body. While sweating is your body's cooling mechanism, if the sweat begins to saturate your clothing, the heaviness of the fabric stifles your skin and causes you to overheat more quickly. Base layers keep your skin dry, and that keeps your clothing dry, which ultimately makes you as cool as possibly on a hot day.

The Craft proCOOL Mesh sleeveless base layer is their fastest-wicking base layer. It's a warm-to-really-hot weather piece made from multi-channeled, hollow fiber polyester filaments that exponentially increase moisture absorption and the release of warm body heat. A mesh knit creates more air pockets across the surface of the fabric, maximizing ventilation and air to skin contact. Even as temperatures soar, proCOOL keeps you dry and comfortable. It's why you see top-notch pro teams wearing Craft base layers no matter how hot it gets (and no matter who their clothing sponsors is). When they unzip their jerseys, you'll see that tiny "Craft" logo on the base layer right beneath their sternal notch.

If we had a base layer FAQ, this question would be on there: Why choose the proCOOL Mesh Sleeveless instead of the proCOOL T or the proCOOL Superlight? The answers are pretty straightforward:

The proCOOL T is ideal when the temps aren't so darn hot, say 50-75 degrees. The proCOOL T is NOT just a short sleeve version of the proCOOL Mesh sleeveless. The Mesh Sleeveless has a full-mesh construction, whereas the proCOOL T uses standard proCOOL throughout most of the piece, and mesh proCOOL in the sidepanels only. Because of this, the ventilation of the proCOOL Mesh sleeveless is superior. Conversely, the insulating properties of the proCOOL T (on milder days) is superior.

By comparison, the proCOOL Superlight has a wider honeycomb mesh fabric than the proCOOL Mesh sleeveless. It gives a greater feeling of ventilation and air permeability. On blisteringly hot days, the Superlight will provide superior airflow to your skin. With the proCOOL Mesh sleeveless you get Craft's best rate of moisture transfer -- and some cyclists would argue that this ultimately leads to a cooler core body temperature than a less-dry but better-ventilated alternative provided by the Superlight.