Graded-index fiber in a loose-sheath cable experiences optical power losses due to bending at cold temperatures. This bending is due to the more rapid. contraction of the loose sheathing relative to the fiber. The bending produces localized. changes in the density of the glass which disturb the waveguiding effect of the graded-index fiber and decrease the transmitted optical power. In recent experiments fiber optic cables have been tested at temperatures ranging from -100°C to +23°C. Significant but reversible optical power losses and a marked hysteresis have been observed. when SIECOR 122 and 222 cables have been gradually cooled from room temperature to -100°C and then returned to room temperature. Cables ranging in length from 9 to 24 m have been tested, giving an average increase in attenuation at -100°C of 0.150 db/m.