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MJC

In article ,
says...

Most metallic conductors are Zero-Resistance at cryogenic
temperatures.
So, a wire-wound resistor may drop off to near-zero in liquid
nitrogen.

If only superconductors for liquid N2 temperatures (77K, -196C) were so
common! Even at liquid He (4.22K, -270C) only a minority of metals make
the transition.

My Kaye and Laby says: "At low temperatures the effects of impurities
etc become increasingly important and these largely determine the value
of the residual resistance to which many metals decrease at low
temperature."

Mike.