Helium is sensitive to temperature changes. Cold air causes the helium to shrink, which makes the balloon appear to deflate, although it still floats.
Heat can cause the helium to expand and the balloon to burst. For helium balloons to last longer, put it in cooling places (20°C is recommended) and avoid hot
places/surfaces (e.g. car boot, under the hot sun or metal surfaces). Balloons may pop/deflate when the air inside expands much more than it could hold, especially
for foil balloons as the material is non-stretchable.
Avoid direct sunlight as the balloons may pop within an hour. The same result may occur indoors if balloons are exposed to direct sunlight through windows.
Exposed to outdoor conditions, balloons will oxidise and clear balloons become cloudy quickly. Balloons will pop/deflate when it rains so always find a shelter.
Very cool environments may cause helium molecules to shrink, reducing the size and float time of balloons.
Do not place balloon in poor-ventilated places as it escalates the rate of deflation of the balloon. It is definitely not a good idea to leave them in a hot car for a long time.
This is because helium molecules get expanded and balloon will eventually pop.
Indoors or outdoors, the constant flow of air around a balloon will increase the speed at which helium molecules escape through the wall of the
balloon, resulting in reduced float time.