The FisherbrandTM Polypropylene Centrifuge Tubes, 15mL, Sterile, Bulk Pack, 500/Pack are made of clear polypropylene plastic with blue graduations. They have a screw cap and an O-ring for leakproof closure. The tubes have a working volume of 15mL and can withstand centrifugal forces up to 5,000 x g. They are sterile and individually wrapped. The pack contains 500 tubes. These tubes are suitable for centrifuging biological fluids and can be used for sample storage. The polypropylene construction makes them lightweight and resistant to most chemicals.