Superfluidity is a state of matter, like solid, liquid or gas, in which the viscosity of a fluid vanishes, while thermal conductivity becomes infinite. So the substance, which looks like a liquid, will flow uncontrollably, and also will be at exactly the same temperature throughout itself. Despite the first of these peculiarities, it still has a surface tension, so will rise up the sides of a vessel in which an amount of the substance is placed, but will do so without restriction, and will move right up the sides of the constraining vessel and over the top. So you can't put it in a beaker on a bench: it would escape. To put it another way, these unusual effects are observed when liquids, typically of helium-4 or helium-3, overcome friction in surface interaction at a stage (known as the "lambda point", which is the temperature and pressure, for helium-4) at which the liquid's viscosity becomes zero. Also known as a major facet in the study of quantum hydrodynamics, this effect was discovered by Pyotr Kapitsa, John F. Allen, and Don Misener in 1937 and has been described through phenomenological and microscopic theories. In the 1950s Hall and Vinen performed experiments establishing the existence of quantized vortex lines. In the 1960s, Rayfield and Reif established the existence of quantized vortex rings. Packard has observed the intersection of vortex lines with the free surface of the fluid, and Avenel and Varoquaux have studied the Josephson effect in superfluid 4
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