An inflation balloon 1 comprising a compliant balloon wall 3 and a first 5 and second 10 set of non-compliant filamentous members embedded in the balloon wall. The filamentous members are arranged to be slack so as to allow inflation of the inflation balloon, but to restrain the balloon to an expanded diameter when all of the slack has been taken up by expansion of the balloon. The first filamentous members undergo controlled failure to expand the balloon to a second larger expanded size.
