FIFI was the name given to this German team's detector. Typically, it was double cryogenically cooled - liquid nitrogen used to cool the inner dewar of liquid helium.

Some detectors used a triple dewar with helium-3 and helium-4, resulting in a system that operated in the neighborhood of 0.2 degrees Kelvin. This extreme cold was necessary to keep thermal noise from swamping the extremely weak signals being detected from the edge of the universe.