The Reinforcement is a Habitat compartment that increases its hull integrity. They are constructed with the Habitat Builder and raise the integrity value by seven units. They can be placed on the side-panels of Basic Compartments, T Compartments, Moonpools and Multipurpose Rooms.
Interestingly, when a Reinforcement is placed on a corner of a Multipurpose Room, the hull strength is instead raised by fourteen points as opposed to seven. It is currently unknown whether or not this is a bug.