An apparatus is configured to be positioned between a boss and a shell of a pressure vessel. The boss includes a bore therethrough, and the bore has a longitudinal axis. The apparatus includes an annular body and a gas permeable feature. The annular body includes an inner surface configured to abut the boss and an outer surface configured to abut the shell. The annular body has opposite first and second ends relative to the longitudinal axis. The gas permeable feature is provided on the inner surface and extends at least from the first end to the second end. The disclosure also describes a pressure vessel including a shell, and boss, and an apparatus positioned between the boss and the shell. A method for forming a pressure vessel includes mounting a boss on a mandrel, positioning an annular fitting about a neck of the boss, forming a liner, and forming an outer shell.