Corning disposable glass centrifuge tubes are manufactured from PYREX Type I borosilicate glass, which has more consistent uniform wall thickness. Tubes are ungraduated and available in two styles: threaded for disposable phenolic screw caps, or with a tooled rim for secures snap cap sealing. Caps are sold separately below. The disposable polyethylene snap-caps are manufactured to rigorous standards to ensure a leak proof seal. For screw caps, select either disposable phenolic caps with rubber liners, or reusable screw caps with PTFE liners for improved chemical resistance.