Balloon Care: Foil Balloons are sensitive to extreme temperature changes. In cold air, they may appear deflated; warm air should expand them again. Extreme heat could cause the helium to expand and burst the balloon. Once inflated with helium, this balloon will float 1 week and can be refilled. Foil balloons may conduct electricity. Do not release helium-filled foil balloons outdoors or use near overhead power lines. Use only non-metallic ribbon and attach the balloon to a weight to keep it from floating away.