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.
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.
This is because helium molecules get expanded and balloon will eventually pop.
balloon, resulting in reduced float time.