Katsunuma discussed the difference between the Sony Xperia Z, which he says uses a plastic frame, and the Xperia Z Ultra which uses aluminum side plates. This allowed Sony to make it thinner than the Xperia Z. The latter is 7.9mm thick while the Xperia Z Ultra weighs in at 6.5mm thick. Another difference between the two high-end models revolves around the color purple. Both can be purchased in black, white and purple although the 6.44 inch model uses a solid purple instead of the glittery purple used on the Sony Xperia Z. The reason? It seems that a solid purple color just looks better on the larger model.
So why choose a 6.44 inch screen? Why not round it off to 6.45? Katsunuma said that the 6.44 inch screen happened to perfectly fit a body that would be the thickness and length of a passport. Sony was aiming for that size because many travelers put their passports inside a coat pocket and have it with them at all times while on the road. And by allowing the use of a regular pen to scribble on the glass, travelers using the device won't have to carry around a stylus. While the screen is not made of Gorilla Glass, it is supposedly just as tough.