Mavic's open mesh polyester short sleeve baselayer for hot weather is so light you hardly feel it’s there. It’s stretchy enough to give a close fit and all the seams are flat-stitched so they feel comfortable next to your skin.
Worn under a short sleeved jersey, it wicks sweat really effectively without getting heavy, while all those holes let plenty of air flow through to keep you cool and comfy. A great fabric.