ForeverSafe Polyethylene Burial Urns and Cemetery Vases. Some of the features include ¼” wall thickness, molded in threaded inserts with stainless steel security screws, waterproof, and unlike many urns, may be buried without an additional urn vault. With the worsening economy theft, of cemeteries is on the rise. Polyethylene deters the theft of an item that can never truly be replaced. Urns and vases are available in a variety of colors including granite and metallic like effects.