A machine for converting a sheet stock material into a relatively less dense dunnage product includes both (a) a helical pre-form assembly having a cylindrical mandrel with a longitudinal axis and a guide member for guiding the sheet stock material from a supply thereof into a helical path along and around the mandrel so as to form a helical pre-form that rotates around the longitudinal axis and advances parallel to the longitudinal axis; and (b) a restriction in the path of the pre-form that slows the advance and rotation of the pre-form past the restriction, the restriction causing the pre-form to retard longitudinal advancement, to twist upon itself, and to permanently deform as it moves past the restriction, thereby longitudinally and helically crumpling the pre-form.