How are balloons made?

1. A balloon stretches to many times its size and snaps right back. That stretchy skin is rubber, and it starts as the milky sap of a tree.
2. Workers cut a thin, slanted groove in the bark of a rubber tree. White sap, called latex, trickles down the groove into a cup. The cut is shallow, so the tree keeps growing.
3. A mold shaped like a small balloon is first dipped in a salty liquid that makes latex cling. Then it dips into colored latex and comes up wearing a thin, even coat.
4. Spinning brushes roll the top edge of the wet coat down into a ring. That rolled ring is the balloon's lip, the firm part you blow into and tie.
5. The coated mold rides through a warm oven. Heat dries the latex and links the rubber together, so it becomes strong and springs back when it is stretched.
6. Finally a puff of air and a gentle pull slide the balloon off its mold. The mold goes around again, and the new balloon is ready to blow up.

Tap a station and the mold travels there to show what happens.

• Balloon mold. The mold, called a form, is shaped like a balloon that has not been blown up. The latex coat takes its shape.
• Coagulant tank. The first tank holds a salty liquid. A thin layer of it on the mold makes the latex cling and turn from runny to jelly-like.
• Latex tank. This tank holds colored liquid latex. The mold dips in and comes out with a thin coat. A longer dip makes a thicker coat.
• Lip-rolling brushes. Two spinning brushes roll the top of the wet coat down into a ring. That ring is the lip you blow into.
• Curing oven. Heat in the oven dries the coat and links the rubber together. Now it stretches and snaps back instead of tearing.
• Stripping station. A puff of air gets between the balloon and the mold. The balloon slides off and drops into a basket.

Drag the mold down into the latex and hold it there, or set the dip time and press Dip. Then see how the balloon does when it is blown up.

Experiment: What happens to a balloon whose mold was dipped for only a moment?

1. Set a very short dip and press Dip. Watch the balloon being blown up.
2. Try a dip in the middle.
3. Try the longest dip. How big does that balloon get?

What we found: A quick dip leaves a coat that is too thin, so the balloon pops as it is blown up. A medium dip gives a skin that stretches wide and holds. A very long dip makes a thick, stiff skin that is hard to blow up and uses far more latex.

Turn on JavaScript to try it yourself.

The machines are mixed up. Tap them in the right order to turn the bare mold into a finished balloon.

Most party balloons are made of natural rubber. It comes from the rubber tree. When a worker cuts a thin groove in the bark, a white, milky sap called latex trickles out and is caught in a cup. Latex is mostly water, with tiny bits of rubber floating in it.

At the factory, color is stirred into the latex. Then molds shaped like small balloons are dipped. First they go into a salty liquid, which makes latex cling. Then they go into the latex itself, and each mold comes out wearing a thin, wet coat. A longer dip gives a thicker coat.

Next, spinning brushes roll the top edge of the coat into a ring. That is the lip you blow into. Then the molds ride through a warm oven. The heat dries the coat and ties the rubber together, so it becomes strong and stretchy instead of soft and sticky.

Last, a puff of air loosens each balloon and it is peeled off its mold. The chocolate-dipped strawberry comparison works for the dipping, but not for the end: chocolate sets by cooling and stays on the strawberry, while rubber is set by heat and peeled off.

Key words

Latex

The milky sap of the rubber tree: water with tiny bits of rubber in it.

Form

The balloon-shaped mold that is dipped. The balloon is made on its outside.

Coagulant

A salty liquid that makes latex cling and thicken on the mold.

Curing

Heating rubber so it becomes strong and springy.

Elastic

Able to stretch and then spring back to its old shape.

Check your thinking

1. What is latex?

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   Milky tree sap with tiny bits of rubber in it. Latex is the white sap of the rubber tree. It is mostly water with tiny bits of rubber floating in it.

2. A mold is left in the latex for longer. What happens to its coat?

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   The coat gets thicker. The longer the mold stays in, the more rubber gathers on it.

3. Why are the coated molds baked in an oven?

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   Heat makes the rubber strong and springy. Heat dries the coat and links the rubber together. Without baking it would be weak and sticky.

4. What would happen if the mold skipped the salty liquid?

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   The latex would not cling well, and the coat would be too thin. The salty liquid is what makes latex cling and thicken on the mold.

5. What is the rolled ring at the top of a balloon for?

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   It is the firm lip you blow into and tie. The rolled lip is thicker and stronger, so it does not tear when you blow or tie.