A: When filled with helium, a regular size 11" latex balloon will usually last around twelve hours and then start to deflate. A foil mylar balloon will usually last 4 to 5 days before it starts to deflate slowly. Times based on indoor usage in room temperature environments. Heat and humidity are the enemies of helium and balloons. If you need your balloons to last longer, we may be able to utilize air filled balloons. If air filled are not an option for your application, for an additoanl charge we can treat your balloons with Hi-Float to increase the float time.