Bio Plas 4004 400uL Snap-Cap Microcentrifuge Tubes, Natural Polyethylene. These Snap-Cap Microcentrifuge Tubes give a firm, dependable seal and its tough virgin-polypropylene construction withstands the rugged G-forces of high-speed centrifugation. Use it with confidence for specimen collection, mixing, electrophoresis sampling/handling, enzyme assays, radioassays, immumoassays and many other applications. The smooth, conical interior that lets you remove your entire sample with ease, and without material hangup. You can even cut it to remove a spun pellet. The Snap-Cap is attached to each tube, and the entire unit is autoclavable at 250°F at 15 psi for 15 minutes.