A vbox's unbounded maximum width and height are an indication to the parent that it may be resized beyond its preferred size to fill whatever space is assigned to it. VBox provides properties for setting the size range directly. These properties default to the sentinel value USE_COMPUTED_SIZE, however the application may set them to other values as needed: vbox.setPrefWidth(400); Applications may restore the computed values by setting these properties back to USE_COMPUTED_SIZE. VBox does not clip its content by default, so it is possible that childrens' bounds may extend outside its own bounds if a child's min size prevents it from being fit within the vbox.