Helium is used by the Balloon Industry to fill Latex and Foils.
Here are some facts about how long they last.
11" Latex Balloons last for 6 to 8 hours depending on the environment.
Hot they will expand and pop.
Cold they will become small but if you bring them to an warmer area they might perk up.
36" Latex Balloons last around 24 hours depending on the environment.
You can pre-treat them with Hi-Float that will coat the inside of the latex balloon and the 11" Latex balloon can last for 24 hours or more.
Now with the 36" pre-treated they can last 1 to 2 days.
5" Latex Balloons only 2 hours.
9" Latex Balloons about 4 hours depending on environment.