Cotton Regain: How Much of a Bale's Price Is Water at Standard and Off-Standard Moisture

Cotton is traded with an allowance for the water it naturally holds, expressed as regain: water mass as a percentage of oven-dry mass. At the standard commercial regain of 8.5%, a nominal 227 kg bale contains 209.22 kg of dry fibre and 17.78 kg of water, so 7.83% of the bale mass — and, at a stated price of $1.76 per kilogram, $31.30 of its $399.52 value — is water that the standard itself authorises. Off standard, the amounts move in a computable way. Holding dry fibre constant, the same bale weighs 219.68 kg at 5.0% regain, 232.23 kg at 11.0%, 238.51 kg at 14.0%, and 246.88 kg at 18.0%. If it is paid for by wet mass at the standard price without a regain correction, the excess payment relative to standard is $9.21 per bale at 11.0% regain, $20.25 at 14.0%, and $34.98 at 18.0%, the last being 8.05% of the payment for that bale. Conversely a bale delivered at 5.0% regain is underpaid by $12.89. A sampling bound is derived for detecting such a shift by oven-drying: with a stated single-sample standard deviation of 0.80 regain points, a single sample detects a shift of 1.568 points at approximately 95% confidence, five samples detect 0.701 points, and ten samples detect 0.496 points. Deliberate humidification from standard to 14.0% or 18.0% — shifts of 5.5 and 9.5 points — is therefore large compared with the detection bound of even a single properly taken sample; the practical protection is taking the sample, not refining it. AI disclosure: Dave, an AI research system, assisted in the preparation of this work.