Your turn
Each lab is one step from the video. Change things and see what happens.
Each lab isolates one step, from tree to vulcanised rubber. The models are simplified to show the idea.
Tap the buttons and see what happens.
Drop a ball of plain latex, then one mixed with vine juice. Which bounces?
Compare raw latex with latex treated with Ipomoea alba juice, an early cross-linking trick.
Which ball bounces best?
Bounce heights are a rough picture, not measurements.
Drag across the bark to cut a slanting groove. How long until the cup is full?
Cut a ~30° groove half way round, collect the latex, then open the next panel two days later.
Cut the bark. Watch the white latex drip into the cup.
Add acid, roll it and dry it. What happens to the tiny rubber bits?
Coagulate the particle suspension with acid, sheet it and smoke-dry it.
Add a little acid. Then roll it flat!
Stretch the rubber. Then make it hot or cold. What changes?
Stretch raw polyisoprene at room temperature, warm and cold.
Pull it! Now make it hot or cold.
Chains are simplified; behaviour is a rough picture.
Add sulfur bridges, then stretch the rubber when hot and cold. Does it still spring back?
Toggle cross-links and compare the response across temperatures.
Add the yellow bridges. Now pull it, hot and cold!
Chains are simplified; behaviour is a rough picture.
Slide from the Amazon to England, Asia, an oil factory and your things.
Follow the 1876 seeds to Asia, then compare natural and synthetic rubber.
Slide along. Where does rubber end up?
Rubber comes from a tree! The rubber tree has milky white juice under its bark. The juice is called latex.
Early in the morning, a tapper cuts a thin line in the bark. White latex drips down into a little cup. The tree is not cut down. It keeps making more latex for many years.
Latex is mostly water, with tiny rubber bits inside. Add a little sour acid, and the bits stick together, like lumpy milk. The lumps are rolled flat and dried into sheets.
Inside rubber are long, wiggly chains, like spaghetti. Pull, and they go straight. Let go, and they curl up again. That is why rubber stretches and snaps back.
Plain rubber gets sticky when hot and stiff when cold. Cooking it with a yellow powder called sulfur makes little bridges between the chains. Now it springs back on hot days and cold days.
Natural rubber comes from latex, a milky white liquid that oozes out when you cut the bark of the Pará rubber tree (Hevea brasiliensis). The tree is native to the Amazon rainforest in South America.1 Almost all natural rubber, about 99%, comes from this one species.3
Today, though, about nine out of ten tonnes of natural rubber are grown in Asia, not South America,3 and more than half of all the rubber made in the world isn't natural at all. It's synthetic rubber, made in factories from chemicals that come from oil and natural gas.1
Getting latex out is called tapping. Before sunrise, a tapper uses a special knife to shave a thin groove into the bark. The groove slants downward at about 30° and goes about halfway around the trunk.23 Latex seeps out, runs along the groove, and drips from a little spout into a cup tied to the tree. Later in the day, the tapper comes back to collect it.3
Each tapping gives about a cupful of latex, holding roughly 50 grams (1.7 ounces) of solid rubber. Trees are tapped about once every two days, and each new cut is made just below the last one.2
The tree is not cut down. It starts giving latex at 5 or 6 years old and, with care, can keep going for more than 20 years.2 Wild rubber trees can grow 34 metres (120 feet) tall; plantation trees stay nearer 24 metres (80 feet).1
Not quite. Latex flows in its own special tubes, called latex vessels, in the inner bark. Scientists still aren't completely sure what it's for, but it seems to help the tree heal by covering wounds, a bit like a scab.23 The rubber tree's tubes are connected into a network, so one cut drains latex from a big area. That's why it beat other latex trees as a rubber crop.3
Latex is mostly water. Floating in it are countless tiny particles of rubber, each about half a micrometre across, far too small to see. Rubber makes up about 30% of the latex.2
| Step | What happens |
|---|---|
| 1. Tap | Latex drips from a groove in the bark into a cup2 |
| 2. Coagulate | A mild acid (formic acid) makes the rubber particles clump into crumbs, like milk curds2 |
| 3. Press | Rollers squeeze the curds into thin sheets or crumbs and push out water2 |
| 4. Dry | Sheets are dried, often over a smoky wood fire, which stops mould and turns them amber; or crumbs are dried and pressed into blocks2 |
| 5. Ship | Bales and blocks go to factories. About 10% of natural rubber is shipped as liquid latex instead, for things like gloves and balloons2 |
| 6. Compound & cure | Factories mix in other ingredients, shape the rubber, then heat it with sulfur (vulcanisation) to fix its shape and make it springy157 |
Rubber is made of incredibly long chain molecules. In natural rubber, the chain is called polyisoprene: thousands of small units of a molecule called isoprene (C5H8) linked together.54 Materials made of long chains are called polymers, and stretchy polymers are called elastomers, short for "elastic polymers".4
This is the "aha". Normally, each rubber chain lies in a loose, random coil, like a strand of cooked spaghetti. When you pull, the chains straighten out in the direction you're pulling. When you let go, the jiggling of their atoms makes them wriggle back into random coils, so the rubber snaps back.4 Natural rubber can be stretched to seven or eight times its length.5
Plastics are polymers too, but in most plastics the chains are too crowded or stiff to move like this, which is why a plastic bottle doesn't bounce back like a rubber band.4 (Read how plastic is made to compare.)
Raw natural rubber has a big weakness: its chains are only tangled, not tied together. In warm weather it softens, and above about 50 °C (120 °F) it turns tacky and loses its springiness, because the chains can slowly slide past each other. In the cold it stiffens, and it can crystallise and go hard.5 Early rubber raincoats and shoes were famous for turning sticky in summer and cracking in winter.36
Vulcanisation means heating rubber with sulfur. The sulfur atoms join onto the chains and form tiny bridges, called cross-links, between neighbouring chains.7 Now the chains can still uncoil when you pull, but the cross-links stop them sliding past each other, so the rubber springs back into shape.1516 Vulcanised rubber is stronger, resists wear, and stays elastic over a much wider range of temperatures.7 Modern factories vulcanise at about 140–180 °C.7
The process was discovered in 1839 by the American inventor Charles Goodyear. He had been trying for years to stop rubber going sticky, and had bought an idea from Nathaniel Hayward, who found that sulfur made rubber less tacky. As the story goes, Goodyear accidentally dropped some rubber mixed with sulfur onto a hot stove. Instead of melting, it turned tough and stayed springy.6 Sadly for him, others made fortunes from his discovery, and he died in debt.6
Vulcanisation is what made rubber tyres possible. Today, more than half of all rubber goes into tyres for cars, trucks, bicycles and planes.1
In the explainer's stretch toys, the chains are simplified and the way they react to heat and cold is a rough picture, not measured data.
Long before Goodyear, people in Mesoamerica (today's Mexico and Central America) were making rubber. Archaeologists found a dozen rubber balls in an ancient swamp at El Manatí, in Mexico, dated to about 1600 BCE.10 Some Mesoamerican balls were as big as beach balls and weighed up to 7 kilograms. They were used in a ritual ball game.8
These people didn't use the Pará rubber tree. They tapped a local tree, Castilla elastica, and knew that its latex on its own is sticky and dries brittle. So they mixed it with juice from a morning glory vine (Ipomoea alba). Researchers at MIT tested this recipe in 1999 and found it makes the rubber tougher and much bouncier.8 The vine juice contains sulfur compounds that may help link the chains, a little like a gentle version of vulcanisation, more than 3,000 years early.8 The Aztec name "Olmec" even means "rubber people".9
The name "rubber" came much later: in 1770, the English chemist Joseph Priestley noticed the stuff could rub out pencil marks.1
Rubber trees grow best where it is warm and wet all year, with no frost and about 2,500 mm (100 inches) of rain a year, as in the tropics.1 For most of the 1800s, nearly all rubber came from wild trees in the Amazon.3 Then, in 1876, Henry Wickham took about 70,000 rubber seeds from Brazil to England. Seedlings raised from them were sent to Asia and started the first big plantations there.311 In Brazil, rubber farming was later almost wiped out by a leaf disease, South American leaf blight.13
Today about 90% of natural rubber is grown in Asia.3 The three biggest producers are Thailand, Indonesia and Vietnam, which together grew about 61% of the world's natural rubber in 2022.11 Most of it comes from millions of small farmers working small plots, not giant estates.12 Parts of South Asia and West Africa grow rubber too.1
Synthetic rubbers are made in chemical plants from small molecules, such as butadiene, styrene and isoprene, that come from petroleum and natural gas. These are joined into long chains, just like the chains in natural rubber.14 The industry grew mainly after the Second World War, and today synthetic rubber makes up more than half of all rubber produced.1 Synthetic rubbers can be vulcanised too.1 (Curious where the oil comes from? See how oil is formed.)
Natural rubber is still hard to beat for some jobs. It resists heat build-up, which is why big truck and aircraft tyres use it,112 and most rubber bands are natural rubber because it's so stretchy.17
| Natural rubber | Synthetic rubber | |
|---|---|---|
| Starts as | Latex tapped from rubber trees | Chemicals from oil and natural gas |
| Main molecule | Polyisoprene | Many kinds, e.g. styrene-butadiene |
| Grown / made | Tropics, mostly Asia | Chemical plants worldwide |
| Share of all rubber | Less than half | More than half |
Allergy note: some people are allergic to proteins in natural latex, and it can cause rashes or breathing problems. Latex-free versions of gloves, balloons and bands exist.13
Cut a strip about 2 cm wide from a thin plastic shopping bag (ask an adult to help with the scissors), and find a rubber band of about the same length. Pull each one gently to about twice its length, then let go.
The rubber band snaps straight back: its coiled, cross-linked chains spring back into tangles. The plastic strip stays long and thin, because once its chains are pulled past each other they don't return.4 Skip the rubber band if you're allergic to latex, and never stretch bands towards anyone's face.
Natural rubber comes almost entirely from latex, a milky liquid tapped from the Pará rubber tree (Hevea brasiliensis). But more than half of all rubber made today is synthetic, produced in factories from chemicals made from oil and natural gas.
Natural rubber does. Workers cut a thin slanting groove in the bark of the rubber tree, and latex drips out into a cup. The tree isn't cut down: it can be tapped every couple of days for more than 20 years.
Latex is mostly water with tiny rubber particles floating in it. Adding a mild acid makes the particles clump into curds. These are pressed between rollers into sheets or crumbs, washed and dried. Factories then mix and heat the rubber with sulfur (vulcanisation) to make it tough and springy.
Thailand, followed by Indonesia and Vietnam. Together these three countries grew about 61% of the world's natural rubber in 2022, and Asia as a whole grows about 90%, mostly on small family farms.
Rubber trees need warm, wet, frost-free weather, so the US imports its natural rubber. About 90% of the world's natural rubber is grown in Asia, led by Thailand, Indonesia and Vietnam. The US also uses synthetic rubber, made from chemicals that come from oil and natural gas.
Rubber trees are a renewable crop, but supply is fragile: most trees grow in one region, come from a small number of seeds, and face diseases such as South American leaf blight. Scientists are testing other rubber plants, like guayule and the Russian dandelion, as backups.
Both are made of long chain molecules (polymers). Rubber is a special kind called an elastomer: its chains are loosely coiled and free to wriggle, so it stretches a long way and springs back. Most plastics are stiffer because their chains can't move as freely.
No. During the rubber boom, around 1880 to 1910, many Indigenous people in the Amazon and people in the Congo Free State were forced to collect wild rubber and were treated cruelly. Public outrage helped end the Congo Free State in 1908.
Keep exploring: How is plastic made? · How is oil formed? · How is paper made? · How is silk made?