The name ‘vat’ comes from the wooden vessel which was first used for the reduction and application of vat dyes. Vat dyes are made from naturally not synthetically. Vat dyeing is widely used for coloration of cellulose materials such as cotton. Vat dye can’t be directly applied and required vatting because it is insoluble in water. However, they can be made soluble by reduction in alkaline solution which allows them to affix to the textile fibers. Subsequent oxidation or exposure to air restore the dye to its insoluble form. Indigo is the original vat dye. These dyes are the fastest dyes for cotton, linen and viscose. They are used with mordants to dye other fabrics such as wool, nylon, polyesters and acrylics. But vat dyes fastness properties is good among the all dyes. The dye takes their generic name from vatting. The vat dyes are naturally obtained coloring materials from the ancient time and kept into wooden vat and make soluble in vat by the process of fermentation- so it is called vat dyes.