Much stronger and more resistant to acids, bases, solvent and Heat (-40 to +140°C) than Polypropylene. These durable racks are molded in a single, continuous piece - no assembly required and no detachable pieces. Racks are made of Delrin® fiberglass-reinforced polyoxymethylene (POM), an engineered polymer developed by DuPont to have exceptional chemical and heat resistance. Molded index coordinates and flat labeling areas keep samples organized. Racks made with Delrin are Autoclavable. Choose 20 mm Rack for 15 mL Centrifuge Tubes Choose 30 mm Rack for 50 mL Centrifuge Tubes