Fuzz Buttons consist of a single strand of gold-plated beryllium copper wire compressed into a dense, sponge-like cylindrical shape.
[1][2] The term "Fuzz Button" was originally conceived and trademarked by Tecknit, but is now owned by a Denver-based company called Custom Interconnects.
This kind of connection is used in cases where permanent connection techniques like soldering or non-permanent ones like pogo pins or elastomeric "Zebra" connectors are not suitable, for example due to extreme vibrations or temperatures.
They can also be used where low-distortion signal transmission is needed, like on PCB (board-to-board) interconnects, or in IC testing sockets where additionally many mating cycles are required.
When a mating array for multiple contacts is needed, like for BGA or LGA IC packages, Fuzz Buttons can be placed in thru-holes in an insulated piece of material, such as dielectric plastic.