This study aimed to investigate the relationship between hornification and the accessible surface area for cellulosic pulps in order to obtain a better understanding of the mechanisms behind hornification. Hardwood and softwood paper grades were hornified to varying degrees by sequential high-temperature drying cycles, and the degree of hornification was assessed by water retention, which was shown to decrease linearly and to correlate closely with accessible surface areas measured by xyloglucan adsorption for both hardwood and softwood pulps. The relationship between hornification ratios and accessible surfaces for xyloglucan adsorption shows different linear relationships above and below 100 degrees C, supporting the hypothesis of different hornification mechanisms at different temperatures shown in the previous literature. Furthermore, hornification was shown to cause a reduction in fiber width for softwood pulps and a reduction in fiber length for hardwood fibers.