Brightness is the most-quoted number on a fluff pulp datasheet and the least stable over time. Understanding the drift matters because it determines how much inventory you can safely hold.
What causes brightness reversion
Bleaching leaves a small amount of residual chromophore in the fibre. Over time, and under the right conditions, those groups re-oxidise and the sheet yellowing slightly. Three factors drive it:
- Moisture. Above 9%, reversion accelerates noticeably.
- Temperature. Every 10 °C of storage temperature roughly doubles the reversion rate.
- Time. Reversion is slow but cumulative. Most of the change happens in the first six months.
How much drift is normal
Under good storage conditions — below 25 °C, below 65% RH — a bleached fluff pulp typically loses 1–2 ISO points over twelve months. Under poor conditions it can lose 4–5.
Two points rarely matters for an absorbent core hidden under a top sheet. Four points can be visible in a thin product or a white tissue application.
What to do about it
- Set a receiving specification, not a shipping one. Specify brightness at the point of use, and let the supplier carry the risk of transit drift.
- Rotate stock. First in, first out is the single most effective control.
- Test the oldest pallet each quarter. A single measurement on aged stock tells you more than a full incoming inspection.
The procurement implication
If your product hides the core, brightness drift is a non-issue and you should not pay a premium for brightness stability. If your product exposes it, brightness stability belongs in the specification alongside the initial value — and it is worth asking a supplier to demonstrate twelve-month data, not just a certificate from the day of production.