Paper is hygroscopic. It takes up water from the air and gives it back, continuously, and it does so all the way from the baler to the discharge port. The material is sold by weight. Those two facts together produce more commercial argument than any contamination question.
Why it is structurally different from a contamination dispute
A contamination dispute has a fixed answer. Whatever was in the bale when it was packed is still in the bale when it is opened. The argument is about measurement and interpretation, but the underlying fact does not move.
Moisture moves. A lot baled in a humid month in the Gulf and discharged in a dry one, or loaded in winter and opened in a tropical summer, has genuinely changed between the two weighings. Both parties can measure honestly and get different numbers, and neither is wrong.
Nobody is necessarily lying.
This is the part that makes moisture disputes so persistent. In a contamination argument one side is usually mistaken. In a moisture argument both sides can be right about their own measurement, which is why the contract has to settle the method in advance rather than the number alone.
What a contract needs to say
Most contracts state a maximum percentage and stop. That single figure leaves three questions open, and each one is enough to produce a dispute on its own.
- Measured how. An oven-dry laboratory determination and a handheld meter reading on the outside of a bale are not the same measurement and will not produce the same number.
- Measured where and when. At loading, at discharge, or both? A figure agreed at origin and a figure taken a month later on another continent are measuring different states of the same material.
- And then what. If the lot comes in above the limit, is there a weight deduction, a price allowance, a right of rejection, or a negotiation? Deciding this after the fact is where relationships are damaged.
A contract that answers all four — limit, method, point, consequence — almost never produces a moisture argument. A contract that answers only the first produces them regularly.
Where the water actually comes from
Three sources, in roughly descending order of how often they cause trouble:
- Ambient humidity at the point of baling. The material equilibrates with the air it was stored in. Outdoor or partially covered storage before baling is the single biggest variable.
- Rain exposure during handling. Usually visible as staining on the outer wraps of a bale, and usually confined to them. This is the case most often confused with a systemic moisture problem when it is a surface one.
- Condensation in the container. Temperature swings across a long voyage can move water out of the cargo and back onto it. Loading dry does not entirely eliminate this.
Only the first is really within the seller's control, which is why experienced suppliers describe their storage conditions unprompted. It tells a buyer something a percentage figure does not.
For pulp, the same issue with different arithmetic
Market pulp is normally traded on an air-dry basis, and the convention of pricing against a nominal dryness means the moisture question is handled inside the pricing mechanism rather than argued afterwards. Mill certificates state the figure and the contract references it.
The practical consequence is that pulp moisture disputes are rare and recovered paper moisture disputes are common — not because the physics differ, but because the commercial convention around pulp settled the question decades ago and the recovered paper trade left it to individual contracts.
Four habits that remove the problem
- Agree the measurement method in the offer, not the contract boilerplate.
- Agree the point of measurement, and if it is at origin, agree who witnesses it.
- Agree the consequence of exceeding the limit before booking, as a formula rather than a conversation.
- Describe storage conditions when offering. A seller who volunteers that material was stored indoors is giving the buyer information worth more than a tightened percentage.
Moisture is one of the six defects that commonly put material into off grade, where it is normally workable with an allowance agreed up front. What happens when a dispute does arise is covered in anatomy of a claim.