TPU or not TPU? the quest for the perfect inner tube part 1

Update: this is the first part about the history of inner tubes. The second part compares TPU to other tube materials and provides a complete market overview. Find it here: Part II.

There is a new generation of inner tubes on the market, made out of TPU, much lighter, thinner, and supposedly more puncture-resistant, whilst having lower rolling resistance, saving you precious watts. One of these tubes made by Tubolito is featured here on YellowCrank. So is all great about those tubes, and should we all be riding them?
I decided to dig a bit deeper.
My research quickly became extensive, so I split the topic into two posts. This is the first one, laying out the background and history of inner tubes and their different materials.

Timeline of inner tube development

1) Latex

Long before Europeans set foot on American soil and overlooked the inconspicuous rubber over immeasurable gold and silver treasures, the natives of Central America – the Aztecs and Mayans as well as other native tribes – knew how to form various and useful things such as balls and bottles from the milk of what they called the “weeping tree.”
In 1495 Christopher Columbus was the first European who, on his second voyage to the new world, saw native Haitians play with an elastic ball.

Harvesting of natural rubber

Another 250 years passed before the existence of rubber was again reported by the French naturalists CM de la Condamine and CF Fresneau in 1751.

In 1763 PI Macquer and LAM Herissaut found that rubber was soluble in ether and turpentine and that after the solvent had evaporated, it showed the same properties again as before the dissolution. With such solutions, Macquer coated wax molds, and by melting the wax, they made the first molded articles such as rubber hoses and rubber shoes. An industry started, and among other things, the physicist JAC Charles used rubber to seal textiles to manufacture the first hot air balloon by the brothers Montgolfier in 1783.

By 1830, the world’s rubber consumption had grown to 150 tons. The rubber was still raw, gooey, and sticky when hot and hard and brittle in winter temperatures. Then came a breakthrough: In 1839, Charles Goodyear, an American chemist, found that mixed with sulfur rubber turns into a completely new substance when exposed to a certain amount of heat. This process is called vulcanization and laid the foundation of modern rubber as the resulting rubber was vastly superior: it kept the same properties independent from temperature. Rubber demand exploded, and in the 1860s, Brazil’s rubber monopoly drove prices up to the extent that rubber became more expensive than silver.
That led to several daring smuggling attempts of seeds of the rubber tree, and in 1876 those attempts were successful, and seeds were finally smuggled out of Brazil. In the subsequent years, plantations were successfully started in Southeast Asia, which is until today the region where the vast majority of all-natural rubber is being produced.

The world’s rubber consumption continued to grow fast, and in 1910, the world’s consumption was already at 100,000 tons. Then came Irishman John Dunlop. He patented and popularised the pneumatic tire. Wheel and tire design patents and products exploded. Natural rubber always played an essential role in providing the airtight casing throughout all iterations, be it in car or bicycle tires. Today the tubes made from natural rubber are called “latex tubes” as latex is often (and incorrectly so) used to refer to natural rubber.

2) Butyl

Since the beginning of the 20th century, German and American chemists have been working on synthesizing rubber. Several discoveries and new materials were made; however, all of them to more or less extent of lower value than natural rubber.
Then came World War II and the Japanese occupation of significant parts of Southeast Asia. Suddenly, over 90% of all rubber plantations were under the control of the axis forces. The United States, which had recognized this threat early on, had already begun to invest massively in the science and manufacturing of synthetic rubber, and butyl rubber was one result of those efforts. By 1943, it was ready to be commercialized. The primary attributes of butyl rubber are excellent impermeability/air retention and good flex properties.

Example of a recipe for inner tubes made from butyl. In addition, other chemicals are involved in the manufacturing process.

In 1960 synthetic rubber for the first time surpassed natural rubber production with 2.65 million tons vs. 2.08 million tons. Butyl was now everywhere, from car tires to car and bicycle inner tubes and many other consumer goods and industrial applications. For competitive cycling, however, tubulars were still the only choice in the sixties and seventies, and they typically have a latex (natural rubber) inner tube. This started to change when Michelin introduced the Elan clincher tire in collaboration with Mavic, who provided the matching rims. That product was so successful that for Mavic, sales of clincher rims went from 5% to 95% within a few years. Butyl inner tubes that had already dominated the casual bicycle market by this point now also made inroads into competitive cycling.

Despite all the advances in developing new synthetic rubbers, natural rubber retains its importance to this day. It is an all-around rubber since the sum of its properties is not surpassed by any synthetic rubber. As of today, natural rubber constitutes around 40% of all rubber production.

3) TPU

After WW1, Germany was cut off most natural rubber and intensified research into synthetic rubber and rubber-like substances. One of the outcomes was the invention of polyurethanes (PU) by Rr. Otto Bayer in 1931.
It took until 1969 to develop thermoplastic polyurethane (TPU) at the company Bayer. The “thermoplastic” in the name refers to the material being able to be melted and shaped. It is, in a sense, a further development of PU but also inherently different. TPU has excellent abrasion resistance, ozone resistance, hardness, strength, good elasticity, low temperature resistance, good oil resistance, chemical resistance, and environmental resistance. It sits somewhere in the sweet spot between rubber and plastics regarding its characteristics, such as hardness and elasticity. Typical TPU applications are car instrument panels, skateboard wheels, power tools, drive belts, footwear, outer phone cases, wire and cable jacketing.

In 2010 inner tubes out of TPU started to appear from two companies, Taiwanese outfit FOSS Worldwide and a Swiss company called Eclipse International AG. Eclipse also filed for a patent, specifying the material TPU and a maximum thickness. While Eclipse went after the performance market with thin and lightweight tubes, at 29g for a 700cc version, Foss introduced heavier, cheaper versions. Both brands, however, struggled to gain traction. For Foss, who is still around and markets their tubes as an environmental alternative to butyl, there were reported cases of separation of the two ends of the tube cylinder that are fused. Eclipse had a different problem; their tubes were costly (around USD 50 per tube), proved too delicate, and had some valve stem issues, so they disappeared from the market within a few years.

Then a big brand entered the market. In 2015, German company Schwalbe introduced the Evolution inner tube at Eurobike. Their material of choice was a TPU from BASF, called Aerothan. The tubes were available for mountain bikes with disc brakes only, as they could not take the heat resulting from extended braking with rim brakes. They also did not last on the market and disappeared after a couple of years.
One year later, in 2016, TPU tires were brought into existence again by the Austrian company Tubolito. Their tubes are known for their bright orange color and are offered in a super lightweight version (for disc brakes only) and a “regular” lightweight version.
The same year a German company, TPU Plus GmbH, launched REVOLOOP, another new entry into the TPU tube market.
In 2020 Schwalbe relaunched their TPU inner tubes, calling them Aerothan this time, like the material from BASF that’s being used. This time around, their tubes are suitable for both disc and rim brakes.

Will TPU inner tubes dominate the market in the future, similar as butyl tubes do now, or will they disappear again? That Schwalbe went for a second effort after the first one failed shows, they believe in and bet on the potential.
In a following post, I will explore the benefits of TPU inner tubes and the challenges they need to overcome if they want to find wider adoption.

Edit Sep 2021: More brands have jumped on the bandwagon of TPU: There are also TPU inner tubes available from tire brands Wolfpack (since 2018) and Pirelli (since 2021), who chose the color yellow for theirs and call them the Pirelli SmarTubes.