Float time is the number most suppliers are vaguest about, and the one that decides whether an event looks finished or looks like it is packing up.

Latex: eight to twelve hours

An 11 inch latex balloon on plain helium gives eight to twelve hours in a normal room. Helium atoms are small enough to pass straight through natural rubber, so the balloon is losing lift from the moment it is tied.

Heat accelerates it and cold slows it, which is why balloons inflated in a cool store room and carried into a warm hall sag faster than anybody expects. Inflate as late as you sensibly can.

Latex with Hi-Float: two to three days

Hi-Float is a liquid coating applied inside the balloon before inflation. It dries to a thin film that seals the pores, and it multiplies float time by roughly five.

It has to be applied properly and it adds a little weight, so a treated balloon rises slightly less enthusiastically. For an event that starts in the evening and was set up in the morning, it is the difference between a display and a disappointment.

Foil: two to four weeks

Metallised nylon leaks far less than rubber, so a foil balloon holds for weeks rather than hours, and the self-sealing valve lets it be topped up when it eventually softens.

This is why in-store displays and week-long activations use foil almost exclusively, even though the unit cost is higher than latex.

Air-filled: a week or more, and no helium at all

Air does not escape the way helium does, so an air-filled balloon holds its shape for a week indoors and often a fortnight. It will not float, which is why air-filled work is built as garlands, arches and cup-and-stick displays rather than floating clusters.

With many venues no longer permitting helium, this has stopped being the fallback and started being the default.