April 5, 2021

Understanding the difference between optical coverage and shielding factor

The shielding factor (Kr) is used to determine the optical coverage (F) of the braided shielding of a cable.

Often confused, an optical coverage of 85% corresponds to a shielding factor of 0.617. Requiring a shielding factor of 85% would actually correspond to an optical coverage of nearly 97.8%.

Optical coverage/shielding factor

These are two terms used to characterise the braiding of a cable.


Please note: the main term used in cable specifications is optical coverage.


The optical coverage or shielding factor of braided shielding is the ratio of the shielding surface area to the cable surface area.


The effectiveness of a braided shield will depend on the optical coverage.

cable shieldcable shield

How is it defined?

F : Optical coverage

Kr : Shielding factor

Optical coverage and shielding factorOptical coverage and shielding factor

Table of equivalence

The higher the optical coverage, the better the protection:

Optical coverage

F (%)

Shielding factor


60 0.368
65 0.409
70 0.453
75 0.500
80 0.553
85 0.617

Shielding provides protection against both the transmission and the reception of electromagnetic interference (EMC). It works on the Faraday cage principle, whereby any metal cage with an earth connection prevents magnetic fields from passing through it.


Braided shielding is mainly effective against low-frequency electromagnetic interference. For high-frequency interference, shielding with aluminium tape or mixed shielding (aluminium tape + braid) is recommended.


For more general information about cables, find out What AWG means ?