Selection of dye to a particular fiber is based on the fiber content of the fabric to be dyed. Natural dyes are applied to natural fibers by use of mordants to fix them. Using different mordants yields different colours. Among the various synthetic dyes available, cotton can be dyed with direct, napthol, vat, sulphur and reactive dyes. As some colours are not available in one class of dyes, combination of classes can be made for eg. Green colour is not available in napthols so vats are used for obtaining green colour. Similarly selection of dye classes is also made on the degree of permanence and the cost of fabric to be dyed. Direct dyes are cheaper than napthol and napthols are cheaper than vats.
Both wool and silk can be dyed with acid colours which cannot be used on cellulosics. Synthetics like polyester, nylon can be dyed only with disperse dyes while acrylic requires basic dyes.
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