In this paper the relations between the structural changes in the fibers and in the paper and its hygroexpansivity are examined. In particular, the effect on the hygroexpansivity of sheet density attained by wet-pressing or beating has been studied, with special emphasis on the effects of the amount of fines present and of the curliness of the long fibers. It is concluded that curled fibers give the sheet a higher shrinkage potential than straight fibers and thus give sheets with a higher hygroexpansivity when they are dried freely. The addition of fines increases the hygroexpansivity especially for freely dried sheets. A higher density slightly reduces the hygroexpansivity for sheets dried under restraint but increases it for sheets which have been dried freely. A linear relationship between hygroexpansivity and drying shrinkage exists only for sheets wetpressed under similar conditions.