Disclosed are fiber optic assemblies having at least one optical fiber disposed within a tube and/or cavity along with a powder or powder blend that is at least partially mechanically attached thereto. In one embodiment, the powder or powder blend includes a water-swellable component that is mechanically attached to about 30 percent or less of the surface area of the tube wall while still effectively blocking the migration of water along the tube. Other embodiments may have the powder or power blend mechanically attached to the tube, cavity, or the like at relatively high percentage levels of the total powder or powder blend within the assembly, thereby inhibiting unintentional migration along the tube, cavity, or the like. Other embodiments may use powder or powder blends that may or may not include a water-swellable powder to provide other desired characteristics.