Abstract: The invention provides a method of making an elastomeric mandrel for use in formation of parts from composite materials. The method of making includes providing a separable mold with an interior chamber shaped to provide a desired exterior mandrel size and shape; applying uncured elastomeric material to surfaces of the interior chamber of separated parts of the mold; joining the elastomeric material by assembling the mold parts prior to cure such that the material joins at seams and allowing the elastomeric material to cure into a shape of the desired flexible mandrel. The mandrel is provided with a fill opening such that it is fillable with a particulate solid media and evacuable to compact the media.