This invention is an occlusive device for inserting into body cavities or vesicles. More particularly, it is a vasoocclusive device which, as used, is in the approximate shape of an anatomical cavity. It may be ultimately deployed as a substantially spherical shape in the operable configuration. The device is a self-forming shape made from a pre-formed occlusive strand of flexible material. The occlusive strand may be helically coiled or braided and may be adapted with various polymeric fibers. The device is typically introduced through a catheter in the substantially linear inoperable configuration. The invention provides a plurality of such substantially spherical strand portions which nest concentrically with each other in the operable configuration. The invention also includes methods of producing and using the substantially spherical occlusive devices.