Push pull inner cable also called push pull inner wire is a special upgrade of the steel wires rope.
The rope is just able to manage high tensile loads, the push pull inner cable can also transmit high compressive forces.
In fact it is composed of two parts: the inner steel wire rope and the over wrapped flat wire.
This special release includes a built in splined covering that allows a close fit with the conduit inner liner, but with minimum contact. This construction makes the the core run back and forth smoothly like a skater on ice.