Abstract: A device is described that overlays a first fluid, such as blood or a cellular suspension onto a base material, such as a Ficoll liquid density gradient. In some embodiments, the fluid layering device includes a cylindrical reservoir, a fluid barrier, a coupling extension, one or more helical channels in fluid communication with the reservoir, and an exhaust vent. The fluid layering device can be coupled through its coupling extension to an open end of a container, such as a conical centrifuge tube, including the base material. Once attached, the device regulates flow of the first fluid from the reservoir into the conical tube so that a suitable overlay is formed without substantially disturbing a surface of the base material, regardless of the care and skill of the user.