Plastic Centrifuge Tubes are tapered tubes of various sizes normally used in molecular biology laboratories. The centrifuge tubes may vary in capacity from ten milliliters to much smaller capacities as that of micro-centrifuges. The most commonly found tubes are similar in size and shape to a test tube about 10 cm long. Micro-centrifuges usually accommodate micro-centrifuge tubes with capacities in the range 250 μl to 2.0 ml. Such micro-centrifuge tubes are exclusively made of plastic. Plastic centrifuge tubes, particularly micro-centrifuge tubes are less expensive than glass centrifuge tubes. Water is preferred when plastic centrifuge tubes are used. As compared to glass centrifuge tubes, plastic centrifuge tubes are more difficult to clean thoroughly and are usually inexpensive enough that make it a disposable item.