The LNF-ISC4_8A from Low Noise Factory is an ultra-low insertion loss cryogenic isolator that operates from 4 to 8 GHz. It provides an isolation of 22 dB and insertion loss of 0.17 dB. The isolator has been designed to meet the strict requirements of ultra-low temperature physics research. The gold plated OFHC copper body ensures minimum loss and that this loss reaches the lowest possible temperature to minimize thermal noise. The isolator is available in a slim coaxial module that measures 22.3 x 24.6 x 10.2 mm with SMA connectors. Each unit is delivered with actual test data taken at 77 K. Insertion loss improves with 0.07 dB when cooled from 77 to 3 K; all other parameters are unaffected.