The standard commercial moisture regain for cotton is about 8.5 per cent, and cotton yarn is bought and sold on conditioned weight calculated at that figure rather than on the weight that happens to be on the scale when the cartons are packed. Regain is the weight of water held by the fibre expressed as a percentage of its oven-dry weight, so a lot with a measured regain above 8.5 per cent is heavier than its conditioned weight and a drier lot is lighter. Acceptable practice is for the invoice to state the conditioned weight and for any difference between that and the scale weight to be reconciled by a moisture test.
Cotton absorbs and releases moisture with the surrounding air, so the same cartons will weigh differently in a humid mill during the monsoon and in a dry warehouse in winter. Trading on conditioned weight removes that variation and is the convention in ISO and ASTM test methods and in most international yarn contracts.
Why regain matters to the buyer
- You are paying by weight, and a few percentage points of excess moisture on a container of yarn is a measurable amount of water bought at the price of cotton.
- Yarn packed too wet can develop mildew, yellowing and odour during a sea voyage, especially in a container that passes through hot and humid regions.
- Yarn packed too dry is prone to static and breakages on the customer's machines until it reconditions.
- Count and strength are also specified at standard conditions, so moisture affects whether the yarn meets specification, not just how much it weighs.
How moisture is measured and reconciled
The reference method is oven drying of a sample to constant weight and comparing the dry weight with the original, with the result expressed as regain. Mills and laboratories use electronic moisture meters for routine checks and the oven method for disputes. The test should be done on samples drawn from several cartons across the lot, not on a single cone, and the sampling should be recorded on the test report.
In practice, the mill weighs the lot, measures the actual regain and calculates the conditioned weight as the invoice weight. If the measured regain is well above 8.5 per cent, the invoice weight should be lower than the scale weight. A packing list that shows net weight and conditioned weight as the same figure on every carton has not been reconciled and should be queried.
What to put in the contract
State clearly that the sale is on conditioned weight at the standard regain for cotton, name the test method and specify a tolerance within which no adjustment is made. Agree whose test is final in a dispute, which is usually an independent laboratory, and whether the buyer may sample at the time of loading. For blends, the regain is calculated from the proportion of each fibre in the yarn, so the blend ratio needs to be stated too.
For raw cotton bales the same principle applies, although bales are more often traded on gross weight with a moisture limit in the contract rather than on a conditioned calculation. Either way, make sure the basis is written down before the goods are packed.
How Creston & Co helps
We check the mill's moisture testing routine during audits, take sealed samples at loading for an NABL-accredited lab and compare the lab's regain figure with the invoice before you release payment. We also supervise loading so that the cartons sampled are the ones shipped. If you want a second opinion on how a supplier is weighing your yarn, our free 20-minute sourcing review is a good place to start.