- It remains malleable at cryogenic temperatures
- It is soft and pliable so it fills imperfections in mating metal surfaces and creates a hermetic seal
Most materials used for sealing that work at standard operating temperatures will crack and break at the -150C cryogenic temperatures.
Often cryogenic, or any sealing, applications require that a seal be made inside a channel or other feature that isn't always flat and smooth. To illustrate how this works with indium, I used a piece of indium foil to show how it conforms to the surface of this penny.
Read more about indium metal in general or indium wire in particular.