Cellulose is another natural polymer belonging to polysaccharides. The chemical formula for cellulose is also (C6H10O5)n. It has a chemical structure very similar to amylose. Instead of α-d-1,4 glycosidic bonds, cellulose has only β-d-1,4 glycosidic bonds as shown in Fig. 5.2. Due to these β-d-1,4 glycosidic bonds, the molecular chain of cellulose can extend quite linearly, making it a good fiber-forming polymer. In order to use cellulose for sizing purposes, it should be modified to shorten the molecular structure. The two most used cellulose derivatives are carboxymethyl cellulose (CMC) and hydroxyethyl cellulose (HEC).