Tubes: made of strong, highly transparent grade polypropylene Flat-top caps: made of grade polyethylene Plug-seal screw on caps: made of grade polypropylene 50ml conical tubes available; white writing area for easy marking Double threaded design reduces -threading; caps are opened and closed Specifications: Working temperature: stable from -20C to 121C (except flat-) 50ml tubes can withstand centrifugation of 8, 400 and 9, 400 respectively Sealing test: complies with Safety Standards Material: plastic colour: transparent Package Contents: 50 x Centrifuge Tube Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.