Keep your head warm during the colder months. It's very soft and comfortable with a tight weave fabric to keep the wind off. The carbon in the material will stop this stinking after one ride.
SIXS 'original carbon underwear' sounds like something developed for Batman, but it's not just more carbon fibre gimmickry. SIXS have been very smart in their use of carbon. During the fabric production carbon is woven in with the Polypropylene to produce the SIXS patented fabric. Carbon has natural anti-bacterial properties, a real plus for synthetic materials as it almost eliminates odours.
SIXS Carbon underwear can be worn on the bike (and off) for hours without stinking, unlike other base-layers.