This is a Lululemon black and white double stranded headband.
Here is a full view of the front of the headband. You can see the small silver omega Lululemon symbol.
Here are two views of the side. You can see the separate black and white strands.
I have several of these headbands and love to wear these when running or during yoga class. This is the first time that I saw a double stranded one though. I also have this style in pink.