Why do some foil balloons float and others sink?
Two balloons from two suppliers can look identical and behave completely differently: one holds the ceiling for a week, the other is on the floor by morning. The difference is almost never the printing. It is physics plus process control.
The simple rule: lift versus weight
Helium lifts about 1 gram per litre at room temperature. A 18-inch foil balloon holds roughly 9-10 litres, so it can lift around 9 grams of payload — and the balloon itself already weighs several grams. That is why an 18-inch balloon floats on its own but sinks the moment you tie a heavy tassel or a chocolate bar to it.
If your customer says "your balloons don't float", the first question is the size, not the brand.
Four things that actually decide float time
- Film thickness. Thicker metallised PET leaks more slowly but weighs more. A 0.07 mm film is the usual balance for retail balloons; thinner film saves cost and loses days of float time.
- Valve quality. The self-sealing valve is the number one failure point. A cheap valve deforms when the nozzle is inserted and never closes fully.
- Seam strength. Heat sealing temperature that is slightly low produces seams that look fine and creep open under pressure.
- Gas purity and fill volume. Under-filling shortens float time more than anything else. Over-filling stresses the seam.
What to demand from a supplier
Ask for the film thickness in microns, the valve type, and a 24-hour float test result on the actual production batch — not on a sample made months ago. A factory that runs this test can give you a number: "18-inch, filled to 90%, 5 days indoor".
A supplier who answers "all our balloons float well" has not measured anything.
Why this matters commercially
Float time is the only quality attribute your end customer notices. Returns and one-star reviews on marketplace listings are overwhelmingly about balloons that sank, not about print quality or delivery speed. When you compare quotes, a 5% higher unit price that buys two extra days of float time is usually the cheaper option.