What is reeling silk?

In tai chi the body needs to sustain a consistent vector of force in a given direction.
This is achieved by aligning the body so that a path is provided for the force to travel along.

The path is called 'inherent peng'.
It cannot be broken when the body moves or turns, otherwise the ability to transmit power is lost.
Reeling silk is a means of utilising the connective tissues of the body, along with soft muscles, spine and waist - in order to provide this path.
The energy wave needs to use your body as a conduit.
If the channel is weak or tense in any way, the wave will be blocked within.

Your body must be internally strong and loose from the ground to fingertips.