Lululemon Cool Racerback II Heathered Black 

This versatile racerback was designed to stay put and out of your way while you're on the move. Made with Light Luon® fabric that is lightweight, soft, sweat-wicking, and four-way stretch. Light Luon® Light Luon® fabric is a lightweight version of our signature four-way stretch, sweat-wicking Luon® fabric lightweight sweat-wicking four-way stretch cottony-soft handfeel naturally breathable Features Designed for: Yoga Lycra®: Added Lycra® fibre for stretch and shape retention Tight fit: Lets you move without restriction Mobility : Racerback cut for full range of movement no size dot or tag but pit to pit is 13", therefore a sz 4 based on Lululemon sz chart