Achieving high wetfastness is intrinsically more difficult on the cellulosic fibers be- cause of their extreme hydrophilicity. They love water, and offer little protection against water removal to any soluble chemical species which has diffused inside them. This contrasts with hydrophobic fibers such as polyester. Polyester fibers offer water little opportunity to enter until the temperature is almost up to the atmo- spheric boil (see a later chapter on disperse dyes). Dyers and dye chemists have known for a long time that there are only three ways in which dyes can be retained by fibers, and the first two have been used from time immemorial. The three methods are: