Moisture regain
Also searched as: regain, commercial regain, conventional allowance, moisture content, MR
The mass of water a fiber holds, expressed as a percentage of its oven-dry mass, once it has come to equilibrium with a stated atmosphere of temperature and relative humidity.
In detail
Fibers exchange water vapor with the surrounding air until they reach equilibrium. Moisture regain expresses the water held relative to dry fiber mass, so it can be compared across fibers and used to correct traded weights. Hydrophilic fibers with many accessible polar groups, such as wool and cellulose, hold much more water than hydrophobic synthetics. Because equilibrium depends on temperature, humidity and on whether the fiber is gaining or losing water, regain must always be quoted with its conditioning atmosphere.
The science and numbers
Regain R = 100 x (conditioned mass minus oven-dry mass) / oven-dry mass, while moisture content M = 100 x water / conditioned mass, so M = 100R / (100 + R); a regain of 15% equals a moisture content of about 13%. Values are normally quoted for a standard atmosphere, commonly 20 C and 65% relative humidity. Typical figures under such conditions are roughly 14 to 18% for wool, about 11% for silk and lyocell, a few percent for nylon, and well under 1% for polyester, where laboratory measurements on fabrics have reported about 0.2 to 0.4%. Sorption depends on accessible polar groups (hydroxyls in cellulose, amide and ionic side groups in keratin), which lie mainly in less ordered regions, so higher crystallinity lowers regain. Fiber-characterization studies commonly cite ASTM D2654 for regain and moisture content.
A practical example
A wool buyer receives two bales of equal invoice weight, one shipped from a humid port and one from a dry inland store. Laboratory oven-drying shows the first contains noticeably more water. Correcting both to the agreed commercial regain shows the buyer paid for the same amount of fiber only once the water is accounted for.
What to distinguish
Moisture regain is not the same as moisture content, which divides water by total wet mass, and it is not a measure of liquid absorbency or wicking. Values also show hysteresis: a fiber approaching equilibrium from the wet side holds more water than one approaching from the dry side. Commercial or conventional regains are agreed trading values, not measurements of a particular lot.
Origins and history
The word describes the water that oven-dried fiber regains from the air. Because wool, silk and cotton are sold by weight and absorb water, traders needed agreed allowances so that buyers did not pay fiber prices for water, and fixed commercial regains grew out of that need. Wool testing still reports fiber on a conditioned basis: a 2023 study of four Ethiopian breeds, for example, reported raw wool regains of about 9 to 17% alongside clean yield measured to an IWTO standard.
Related terms
Sources & further reading
- Tropical Animal Health and Production: Wool fiber yield and moisture regain of four Ethiopian sheep breeds (2023)
- ACS Applied Materials and Interfaces: Durably hydrophilic and UV protective PET fabric with EGCG and citric acid (2024)
- Langmuir: Controlled electrospraying of sericin nanoparticles on polyester fabrics (2025)
- Polymers: Hygromechanical behavior of polyamide 6.6, experiments and modeling (Wetzel et al., 2023)
Technical references reviewed 2026-09-22. Examples are illustrative. Industry organizations and manufacturers describe their own fields; their references are not independent product endorsements. Figures are approximate and depend on the stated test conditions.