A vacuum insulator having a structure that improves thermal insulation performance, a method of manufacturing the vacuum insulator, and a refrigerator including the vacuum insulator are provided. The refrigerator includes an outer case configured to form an external appearance, an inner case provided inside the outer case and forming a storage compartment and a vacuum insulator provided between the outer case and the inner case. The vacuum insulator includes a core material formed of glass fibers having a diameter larger than or equal to 5 μm and smaller than or equal 8 μm, an adsorbent configured to adsorb a heat transfer medium, and an envelope configured to accommodate the core material and the adsorbent.