These polypropylene test tube racks are designed to be stackable, submersible and to save space! The racks take seconds to assemble and can be stored flat when not in use. At the bottom of each rack are four interlocking feet that allows the units to be stacked on top of one another. The durable polypropylene can be autoclaved and allows the racks to sink at the bottom of water baths. Even in the most agitated water, you will find these racks to maintain their stability. For versatility, the racks come in colors white, red or blue.