A good preform can still make a bad bottle if it is stored or handled badly before blowing. Preforms are robust, but a few storage rules keep them blowing cleanly and protect your yield on the line.
How long do preforms keep?
Stored sealed, cool and dry, bottle-grade PET preforms keep for many months with no meaningful change. They do not "expire" like food, but practise first-in, first-out (FIFO) so the oldest stock blows first and nothing sits indefinitely.
Temperature and condensation — the real risk
The most common field problem is condensation. If cold preforms (from an unheated warehouse or a winter container) are opened in a warm, humid blow room, moisture condenses on the surface and disrupts even reheating — causing haze, uneven walls and rejects. Acclimatise sealed preforms to blow-room temperature for 24–48 hours before opening the packaging. Keep storage out of direct sun and away from heat sources that could soften or deform necks.
Humidity and contamination
Keep the original packaging sealed until use — it protects against dust, insects and airborne contamination that show up as specks or inclusions in the bottle. A dry, clean warehouse is enough; preforms do not need the intensive drying that raw PET resin does.
Stacking and handling
Respect the stacking limit on octabins or cartons — crushed lower layers deform necks and bodies. Avoid dropping or dragging; neck-finish damage is invisible until the cap leaks. Handle bulk preforms gently and keep pallets stable for transport.
Check on arrival
Run an incoming inspection on each batch — neck integrity, weight, colour and any deformation — before it enters storage, so a transport problem is caught early. Delta El Nile for Industry ships every batch with FSSC 22000 V6 food-contact validation; correct storage keeps that integrity through to the blow line.