Float Times Below are the average float times with helium and approximate amount of helium needed according to balloon size. These float times are estimates only. Float times will vary due to balloon shape and environmental conditions such as temperature, weather conditions, and altitude. 18" Foil Balloons3–4 weeks float time. Uses approximately .50 cubic feet of helium per balloon. 26" Foil Balloons3–4 weeks float time. Uses approximately .72 cubic feet of helium per balloon. 36" Foil BalloonsSeveral months float time. Uses approximately 4.00 cubic feet of helium per balloon.