The reasons affecting the moisture regain rate of fiber are internal and external：

1. Internal causes

The role of hydrophilic groups

In the fiber molecule, the number of hydrophilic groups and the strength of hydrophilicity can affect the size of its moisture absorption performance. The more hydrophilic groups, the stronger the hydrophilicity and the better the hygroscopicity; Fibers with low polymerization degree of macromolecules, if the macromolecular end groups are hydrophilic groups, have strong hygroscopicity.

The crystallinity of the fiber

The lower the crystallinity, the stronger the hygroscopic ability.

Fiber specific surface area and voids

The larger the specific surface area of the fiber, the stronger the surface adsorption capacity and the better the moisture absorption capacity; The more pores in the fiber, the stronger the moisture absorption capacity.

Associated organisms and impurities

Different biotics and impurities have different effects. Cotton wax in cotton fiber, oil in wool fiber weakens the moisture absorption ability; The pectin of hemp fiber and the sericin of silk enhance the hygroscopic capacity.

2. External causes

Relative humidity

Under certain temperature conditions, the greater the relative humidity, the better the fiber hygroscopicity.

Temperature effects

In general, with the increase of air and fiber material temperature, the equilibrium moisture regain rate of fiber will decrease.

Air flow rate

When the air flow rate is fast, the equilibrium moisture regain rate of the fiber will decrease.