This top quality line of centrifuge tubes feature flat-top, leak resistant screw caps, a large white writing area and printed graduation marks. Tubes are available with Acrylic, Polypropylene, or Polystyrene construction. The 15mL Acrylic tubes provide a stronger, chemically resistant and scratch resistant surface. Caps are made of HDPE. Sterile tubes are RNase free, DNase free and Pyrogen free.