Why do Balloons deflate?
The latex and Mylar balloons will get deflated with time if they are not treated chemically at the outer surface to stop the internal gas from coming out of the balloon. The balloons that lose air from them will not be airtight. The above two types of balloons have small microscopic holes in the balloon material. If the holes in the material are larger than the gas molecules lying inside the balloon then the gas moves outside slowly and gradually. Effusion is the process of the molecules to move away and come out of the holes of the balloon without contacting the sides of the balloon.
Effusion makes the gas molecules inside the balloon to encounter the walls of the balloon and in turn allows them to move out of the balloon. The rate of deflation of the balloon depends on the kind of material with which the balloon is made and the type of gas that is used to fill the balloon. It is observed by a balloon supplying company at Scotland that the foil balloons filled with Helium were known to float in the air for weeks together. But, these balloons will start to deflate after 3-5 days. The latex balloon was also found to fly in the air for about seventeen hours and can even extend to float if treated again for about few weeks.
Foil and Latex balloons are found to stay longer than the inflated Helium balloons though they do not float in the air. The reason is due to the large size of the gas molecules inside the balloon unable to allow the molecules to pass through the pores of the balloon. The water balloons will not get deflated like that of air balloons which are partially permeable to allow the air to move outside. If a balloon has to be kept floating high up in the sky then the interior of the balloon can be coated to prevent the air to pass out.