Abstract: Disclosed herein, among other things, is a system for constrained layer damping for hearing assistance devices. According to various embodiments, a hollow in-the-ear (ITE) hearing instrument shell is formed. The shell has an air space within a wall of the shell, in various embodiments. A port is created in the wall of the shell. The port is adapted to interface the air space to an area outside the shell, in an embodiment. A viscous fluid is dispensed into the air space via the port, and the viscous fluid is cured within the air space. The cured fluid acts as a constrained layer of mechanical damping within the wall of the ITE shell, reducing audible feedback to a wearer of the ITE.