Moisture regain
Commercial regain
Moisture regain is the weight of water in a fibre expressed as a percentage of its oven-dry weight, and commercial regain is the agreed figure at which yarn of that fibre is bought and sold.
Most textile fibres are hygroscopic: they take up water from humid air and give it back to dry air. Cotton held through a humid monsoon and the same cotton weighed in a dry winter differ in weight even though not a gram of fibre has gone anywhere. For a trade that buys and sells by the kilogram, that is not a detail.
Regain is measured against the oven-dry mass: regain = (weighed mass − dry mass) ÷ dry mass × 100. Moisture content measures the same water against the total, wet mass. The two are not interchangeable — 8.5% regain is about 7.8% moisture content — and hand-held meters display one or the other, so a reading is only useful once you know which it is.
So that buyer and seller are talking about the same quantity of fibre, the trade fixes a commercial (standard) regain for each fibre. Published tables such as ASTM D1909 give widely used figures — 8.5% for cotton, 0.4% for polyester — while viscose and blends vary by table and by contract. A blend's commercial regain is the average of its fibres' regains weighted by their dry-mass share. Where a mill contract states a figure, the contract governs.
Key facts
- Regain R = (W − D) ÷ D × 100, where W is the weighed mass and D the oven-dry mass.
- Moisture content M = (W − D) ÷ W × 100, and R = M ÷ (100 − M) × 100.
- Commonly quoted commercial regain: cotton 8.5%, polyester 0.4%.
- Blend regain: the dry-mass-weighted average of the component fibres' regains.
- Laboratory conditioning uses a standard atmosphere of 65% relative humidity at a controlled temperature (ISO 139).
Who this affects
Yarn traders, spinners, weavers and anyone buying or selling fibre by weight.
How YarnTally handles it
Each organisation keeps a regain table per fibre and per SKU, starting from dated defaults (cotton 8.5, polyester 0.4, viscose 13.0) labelled to be checked against mill contracts. Moisture-meter readings at receipt and at stock count are optional; where one is missing, standard regain is assumed and the line says so. A meter that reads moisture content is converted to regain once, at entry. Stock counts (Business plan) split each line's variance into expected moisture drift and unexplained kilograms.
See what else it doesReviewed September 2026. This is general information about how these rules work, not tax or legal advice, and thresholds and due dates do change. Check your own position with your chartered accountant before acting on it.