In electromagnetic field, dB is the measurement of signal or radiation attenuation ratio in a certain frequency range.

We usually say, this fabric EMF shielding effectiveness / attenuation is >65dB. Then what is dB?

The decibel ( dB) is used to measure sound level, but it is also widely used in electronics, signals and communication. The dB is a logarithmic way of describing a ratio. The ratio may be power, sound pressure, voltage or intensity or several other things. In electromagnetic field, dB is the measurement of signal or radiation attenuation  ratio in a certain frequency range.

BAODING PRETTY TEXTILE nickel copper conductive fabric shielding effectiveness is 71-84dB in frequency range 10-10000MHZ. Our silver fiber fabric attenuation is 50-60dB in frequency range 10 MHZ-3GHZ.