This 28-400 size white polypropylene screw cap has a closed top with a polypropylene/silicone/polypropylene liner. The liner is ultrasonically bonded, making this cap ideal for use with biological media and other sensitive compounds. Case packed with 480 per box. Autoclavable. Cap Material: Polypropylene. Color: White. Liner Material: Polypropylene/Silicone/Polypropylene. Style: Screw Cap. Top: Closed. Cap Size: 28-400. Wheaton #: 240232.