These Corning® Conical Large Volume Centrifuge Tubes are made of polypropylene and have a conical bottom for pelleting and raised graduations. They have Polyethylene plug seal caps and a maximum RCF of 6,000xg. Tubes are sterile and certified nonpyrogenic. Each case has a recyclable foam rack to facilitate handling.Support cushions (Catalog No. 430236 for 250) must be used with this product unless the centrifuge rotor has the appropriate V-bottom cushions.Please check Technical Information Listing for information on the physical and chemical properties of Corning plastic centrifuge tubes as well as important suggestions for safe use.