A: "Mylar star balloons dangle from the ceiling, the pianist strokes her ivories, and waiters . . . waltz through the crowd " — San Francisco Chronicle.
When the party's over, the balloons drift down. "Why?" asks Reader Ben.
Blow helium into a toy balloon and the elastic membrane stretches. The solid-appearing membrane is riddled with microscopic holes. These holes seem huge to tiny helium atoms which careen inside the balloon at speeds of about 2,800 miles per hour.
The molecules collide frequently with each other, zigzagging through the balloon, and sometimes reach the membrane. They may find a gaping hole and zip right through, escaping. That's why balloons deflate.
Let's consider the relative size of latex holes and helium atoms. Manufacturing defects or damage probably create the holes since latex rubber is not naturally porous. The hole diameter is at least 1,000 times larger than that of an helium atom. A helium atom scooting through a latex hole is like a small fly buzzing through a double-car garage door.
You asked if they can make a better balloon, keeping helium in. Mylar is better than latex. Round, latex balloons float for about eight to ten hours. Mylar balloons — the shiny, fancy-shaped ones — last several days as Ben noted.
An ingenious product called HI-FLOAT extends balloon float time to a couple of weeks, at least. The wife of a DuPont chemist had a question like Ben's: "How do I keep balloons up?" Don Burchette, the chemist, invented HI-FLOAT to solve her problem. It only costs about 5 cents to squirt it inside a balloon, and coat the interior.
"An "incredible success", says Duane Smith of Pioneer Balloons, "everyone in the business uses it."
Can they make better balloons? Certainly but not cheaply. NASA pays about $120,000 for a large scientific balloon and uses it only once.
The balloons, however, stay aloft for three weeks. They are made of Stratofilm-372: a special polyethylene designed to hold helium and to withstand extremely cold temperatures (minus130 degrees Fahrenheit, -90 C). The balloons reach 26 miles (42 km), where it gets that cold.
"Very little of the helium passes through the material over periods of two to three weeks while our balloons are flying," says Danny RJ Ball, Operations Manager of NASA's Columbia Scientific Balloon Facility in Palestine, Texas.
(Answered June 6, 2001, updated July 16, 2007)
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