PROBLEM TO BE SOLVED: To provide a cold insulator excellent in safety, high in dispersibility to water in a water retention material and also long in a cold insulation time, and a cold insulator pack using the cold insulator.SOLUTION: Provided is a cold insulator containing water and a water retention material dispersed into the water. The main component of the water retention material is made of fine cellulose fiber, and the volume average particle diameter measured by a laser diffraction method in the water-dispersed state of the fine cellulose fiber is 20 to 175 μm. Alternatively, provided is a cold insulator in which the fine cellulose fiber includes the first fine cellulose fiber and the second fine cellulose fiber, the volume average particle diameter measured by a laser diffraction method in the water-dispersed state of the fine cellulose fiber is 140 to 200 μm, and the volume average particle diameter measured by a laser diffraction method in the water-dispersed state of the second fine cellulose fiber is 15 to below 140 μm.SELECTED DRAWING: None
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