A wipe in a sealed bag is not in suspended animation. The polymer continues to oxidise slowly, the solvent in a pre-wetted pack migrates, and a pallet stacked two metres high compresses the cloth at the bottom. None of this is visible at goods-in, and all of it can put a lot outside its specification before it reaches the bench.
Shelf life is therefore not a single number printed on a box. It is a set of conditions, and the storage rule is what keeps the product inside them.
Three ageing mechanisms
Oxidation. Polyester and polypropylene slowly lose strength as the polymer chain reacts with oxygen. Heat accelerates the reaction; UV starts it. A pallet stored against a south-facing window ages faster than one in a dark, cool store.
Moisture migration. In a pre-wetted pack, the solvent moves within the stack. The top sheet can dry while the bottom sits wet. In a dry pack, humidity is absorbed by cellulose and changes the feel and the residue profile.
Compression. A stack that has been compressed for months takes a set. The fold flattens, the sheet does not open cleanly, and the operator compensates by using two sheets. The product is still within dimensional tolerance and no longer works.
Dry wipes
Sealed knitted polyester typically carries a three- to five-year shelf life from the production date, provided it is stored between 10 and 30 °C, below 65% relative humidity, and out of direct sunlight. The bag matters: a pinhole lets humidity in and lets plasticiser out of the film.
Once the bag is open, the clock changes. A dry wipe in an open bag in an ISO 8 store picks up particles and humidity within a shift. Treat the open bag as a working pack with a shift-level life, not a warehouse item.
Pre-wetted wipes
The unopened shelf life of a solvent wipe is usually 18 to 24 months, set by the solvent and the film rather than the cloth. The limit is loss through the seal and, for water-based products, microbial control.
Open-life is the number that matters on the line. A pack opened at the start of a shift and left unsealed loses solvent and concentrates the remaining solution. If the procedure specifies a 70% IPA wipe, a pack that has been open for six hours may not deliver 70% at the surface. Write the open time on the pack and discard at the end of the shift.
Sterile products
A sterile wipe keeps its sterility assurance only while the barrier is intact. A crease, a scuff or a pinhole in the outer bag is a breach, even if the inner pack looks perfect. Inspect at goods-in and again at the airlock.
Storage conditions matter for the barrier as much as the cloth. Heat and pressure can weaken a Tyvek or film seal. Do not store sterile cartons under heavy pallets, and do not transfer them into a cold room unless the packaging is qualified for the condensation cycle.
| Product type | Unopened | After opening | Critical factor |
|---|---|---|---|
| Dry knitted wipe | 3–5 years | One shift | Humidity, UV, bag integrity |
| Pre-wetted wipe | 18–24 months | One shift | Seal, solvent loss, microbial control |
| Sterile wipe | 2–3 years | Immediate use | Barrier integrity, compression |
Storage rules that are worth enforcing
- Store off the floor on a pallet or shelf, at least 15 cm clear.
- Keep away from skylights and loading-dock doors; UV and temperature swings do the damage.
- Do not stack more than the carton is rated for. Compression is cumulative.
- Rotate stock on first-in, first-out, and record the lot on the pick list.
- Keep the original packaging until point of use. A wipe decanted into an unlabelled bin has lost its lot number.
Record the production date, the lot number and the condition of the outer bag. A one-minute check at receipt prevents a six-month argument about who stored the pallet badly.
When a lot is out of date
Do not assume it is waste. Ask three questions: what is the failure mode, what does the specification require, and can the lot be re-tested against it? A dry polyester wipe at five years and two months may still pass particle and strength tests; a pre-wetted pack at 26 months has almost certainly lost solvent.
If the lot is used for a non-critical task, record the decision and the risk assessment. If it touches a critical surface, re-test or reject. The audit trail matters more than the outcome.
Does freezing extend wipe shelf life?
No. Freezing can damage the fibre structure and, for pre-wetted packs, separate the solvent. Store within the stated range.
Can I re-wet a dried pre-wetted wipe?
You can, but you no longer have a controlled dose or a validated product. Use a dry wipe and a dispenser instead.
How do I prove storage conditions in an audit?
Temperature and humidity logs for the store, plus a goods-in record with lot and date. If the store is not monitored, say so and add a periodic check rather than claiming control you cannot evidence.
If you are writing a storage SOP, we can supply the shelf-life and condition data for every reference in the catalogue.
