At the temperature of liquid helium, near absolute zero, lead becomes a nearly perfect conductor.

A perfect conductor is an electrical conductor with no resistivity.

Resistance is what causes heating in conductors, thus a perfect conductor will generate no heat.

Any external field applied to a perfect conductor will have no effect on its internal field configuration.

In perfect conductors, the interior magnetic field must remain fixed but can have a zero or nonzero value.

Since the ground is not a perfect electrical conductor, ground waves are attenuated as they follow the earth's surface.

Or by a more unformular model which exactly only holds for perfect conductors:

The projector here is the real secret-it makes space itself become a perfect conductor of electric-space-strain.

When I start this, the space between here and that interrupter coil back there will become a perfect conductor.

It apparently is an almost perfect conductor of heat.