Nike have made bike gear for years, and are responsible for dressing Lance Armstrong, so they know a bit about performance cycling.
The Pro Bibs use an innovative multi-panel Swift cut that includes mesh venting strips down the back of the legs and aerodynamic mesh thigh strips around the base of the legs. The mesh panels also come really low on the side of the crotch.
It all looks and feels a bit odd at first compared to normal lycra skinnies, but these shorts are very comfortable over long distances. The venting should really help on hot days too, even if it was chilly during our spring testing period. The pad isn't pre shaped though and it feels bulky in use, which is disappointing for the price.