What foil balloons are actually made of

"Foil balloon" is a trade name, not a material. The real structure is a thin plastic film with a metal layer, and each layer has a job.

Layer 1: the base film

The structural layer is biaxially oriented PET (BoPET) — the same family as the film used for food packaging. It gives strength and a gas barrier. Thickness for balloons typically runs 0.05-0.09 mm; thinner film is cheaper and loses float time.

Layer 2: the metal

Aluminium is vacuum-deposited onto the film in a layer measured in nanometres. That is what makes the balloon silver and reflective, and it is also the barrier that slows helium loss. It is not "aluminium foil" in the kitchen sense — there is no sheet of metal inside the balloon.

Layer 3: the print

Rotogravure ink sits on top of the metallised surface, usually with a white underlay for light colours. Water-based ink is available and increasingly requested for the EU market.

Layer 4: the seam and the valve

Two film sheets are heat-sealed around the perimeter, and a one-way valve is welded into the neck. This is where most failures happen: the seam temperature window is narrow and the valve is the cheapest component to get wrong.

Why the grade matters to a buyer

Two suppliers can quote the same 18-inch balloon at very different prices because they are using different film gauges, different valve suppliers and different sealing speeds. The visible product is identical. The difference shows up at day three.

When you compare quotes, ask for the film structure in writing: base thickness, metal layer, ink type, valve type. A supplier who can name all four is a supplier who controls the process.