Bio Plas 4204 Polypropylene Conical 2.0mL Screw Cap Microcentrifuge Tube, with Skirt, Natural (Pack of 1000) Flat top lid forms an extra-tight seal that will not come open during processing Inscribing patches: all flat top microcentrifuge tubes have a textured writing surface on top of the caps Easy to open with thumb pressure; fully autoclavable for sterile applications Microcentrifuge tubes are manufactured of siliconized polypropylene which provides for extremely low surface adhesion and maximum sample recovery