Screening

Screening is used to reduce the effects of electromagnetic interference (EMI) or electrical noise which can disrupt the transmission performance in some environments. This noise may be as a result of external interference from other electrical equipment or as a result of interference generated within the cable from adjacent pairs (cross talk).

Screens can be:
Aluminium/polyester tape
with a tinned copper drain wire, the most popular construction
Copper/polyester tape
with a tinned copper drain wire, for a better screen effect
Bare copper braid
for electromagnetic interference or when the cable is subject to movements
Tinned copper braid
for electromagnetic interference in presence of corrosive atmosphere or high temperature