[delon]

little background from Extremis comic:

Since Tony Stark has injected himself with nanobots along with the Extremis shot, not only can he have super human strength, speed and healing abilities; he can also connect anytime to data network and access global computer network system. As well, he can command and summon remotely his armor to him and armor up anywhere. Most crucially, he no longer needs to control his armor through verbal command to Jarvis, he basically controls the armor with his thoughts directly. So him and armor is truly one by this stage of evolution.

This armor is made of special metal where it is soft, light & flexible in nature, but with electrical current throughput it hardens. This also explains the "slimmer" slick look of the armor comparing to his previous thick metal versions.