A foil balloon (or Mylar balloon) is an inflatable manufactured from thin metallized polymer films, typically a high-barrier Nylon (PA) film laminated with an LLDPE polyethylene layer and vacuum-coated with aluminum. Unlike a porous latex wall, the foil film is a sealed barrier that holds helium over a multi-day window and supports rotogravure printing.

Helium is required for free-floating applications, such as standard 18-inch rounds, jumbo numbers, and 3D spheres. Air is used for stationary decor, such as arches, backdrops, and stick mounts. An air-filled foil balloon holds its shape for a long period because oxygen and nitrogen diffuse through the film much more slowly than helium.

Insert a smooth pump nozzle 2 to 3 inches into the tail inflation channel, marked by the slip sheet. Inflate steadily to a fraction below full extension to leave room for thermal expansion, then pull the nozzle out and pinch the tail flat. The internal LLDPE flap seals shut.

The retention window depends on the film build, the size, and the ambient conditions. A larger balloon carries a larger helium volume and holds buoyancy over a longer window than a smaller one. An air-filled balloon stays taut for a longer period because the gas molecules are larger. The retention window for a given SKU is confirmed at quotation stage.

A balloon will not float when the upward lift from the helium is smaller than the weight of the film and the valve. Three common causes: a balloon below the practical flotation threshold, a narrow shape that adds seam weight, and a helium supply that is below the purity level a dense foil membrane needs.

Two causes. Cold air contracts helium, which temporarily reduces the fill and reverses at room temperature. A physical leak, from a torn valve or a seam failure, does not reverse. Batch samples from each production run pass an inflation inspection held for a controlled window before packaging.