It's cold at 28,000 feet
Piccard and Borschberg fly at 28,000 feet in an unheated, unpressurized cockpit. They carry oxygen, needless to say. But if it's minus 30 Celsius outside, and minus 15 Celsius inside, that makes it about 5 degrees in the cockpit. Piccard referred to his down jacket and other ski clothing type accessories, but I think the cold would add to the loneliness, once you're flying through dark in the middle of the Pacific. Minus 30 Celsius is about minus 22 degrees Fahrenheit outside.