For much of the world, it's a niche product. In North Korea, where winter temperatures are frigid and which cannot produce enough cotton or wool for clothing, the synthetic fibre developed after nylon was glorified as a revolutionary invention.
Known outside North Korea as vinylon, it was christened "vinalon" by founder Kim Il Sung. He ordered it be developed to put clothes on people's backs.
It's a story which reveals much about the history of North Korea.
The state says the fibre symbolises its self-reliance, but diplomatic records show the project was less successful than Kim hoped — Pyongyang was more dependent on others than it claimed.
The North Korean government does not provide foreign media with a point of contact in Pyongyang and the state's delegation to the United Nations did not respond to a request for comment.
The global vinylon fibre industry was worth $443 million in 2016 and is projected to reach $539 million by 2022, according to Orbis Research. Swedish outdoor clothing company Fjällräven uses a form of vinylon, Vinylon F from Japan, in products including the Kånken backpack.
Fjällräven does not source material from North Korea, a company spokesman said.
Companies in Japan and China make vinylon based on petroleum. But North Korea has no oil reserves. Instead it makes vinalon from two commodities it has in abundance: coal and limestone.
The process starts with workers mining anthracite and breaking limestones.
Vinalon dates back to 1939, two years after DuPont of the United States introduced nylon, and with it affordable stockings, American glamour and movie stars.
At the time, North Korea was part of Japan and nylon was undercutting Japanese silk and cotton exports. A Korean scientist was on the team that developed an alternative fibre. His name was Ri Sung Gi.
Ri's invention starts out as hard, white crystals that look like sea salt. But once drawn out and spun into a thread, it acquires a texture like cotton. It is stiff and hard to dye, but strong.
It was promising. But two wars interrupted Ri's efforts to develop his fabric.
In 1948, after World War Two, North Korea became a Communist state.
The North Koreans invaded the South and in the ensuing three years, the U.S. bombed Pyongyang. Around 2.5 million soldiers and civilians died on both sides, according to South Korea's defence ministry.
In 1953, the Korean War paused with a truce.
Ri wanted to help rebuild. He offered to develop his fabric in South Korea. The South, which was allied with the United States, was not interested.
At this time, all Soviet states were driving for technological prowess. The North was courting foreign scientists, and it did what it could to keep hold of them.
Ri defected. North Korea likened him to Marie Curie, the French chemist who developed the theory of radioactivity.
"To bore a hole into the heart of US imperialism, I have been peering through microscopes and shaking my test tubes with determination," Ri Sung Gi wrote in his memoirs.
JUCHE!
The Soviet Union was forging ahead. On April 12, 1961 Russian Cosmonaut Yuri Gagarin beat America to be the first man in space. Josef Stalin sponsored Kim Il Sung as founder of North Korea.
Under Japanese rule, the North had received more investment in heavy industry than the South and it had ample energy.
But North Korea needed overcoats for its people, Kim told the Soviet ambassador, A M Puzanov. "If we do not solve the clothing problem it will be hard to compete with the South," he said, according to Puzanov's journal. The Soviet Union could not help supply cotton.
Ri had proven in lab tests that vinalon could be made. Kim saw the fibre as a political tool.
He created an ideology of self reliance known as Juche. The word translates literally as "subject," but stands for the notion that man is the master of his own destiny.
Kim said vinalon was the "juche fibre."
"The vinalon industry is the shining fruition that the Juche idea of our Party was reflected in the field of chemical industry," Kim said in 1967.
On May 6 1961, he held an opening ceremony for the February 8 Vinalon Plant in Hamhung, in South Hamgyong province. Kim was telling his allies North Korea could produce 10,000 tonnes of vinalon a year and would soon be producing more than 300 million metres of textiles a year, according to documents in the Wilson Center archive.
The factory, built by a division of the Korean People's Army working on three shifts of 3,000 people, went up so quickly that the triumphal phrase "vinalon speed" emerged in state propaganda.
Looking at the first vinalon strands, Ri said they were "white as snow and lighter than a dandelion puff."
Kim Sung-hee, a North Korean who defected to the South, said she attended the ribbon-cutting ceremony.
"Inside the factory I saw pink and red jackets. Even after 15 years, the vinalon jackets did not get frayed, although the colours could change a bit," she said.
Defectors born before the 1980s said they used to wear jackets, school uniforms and socks made of vinalon.
The fibre was part of an industrial drive like the one Mao Zedong launched in China. North Korea's effort was known as Chollima. Embodied by a Flying Horse, it galvanised workers into skipping breaks to boost productivity, helped by slogans such as "drink no soup."
In 1961 Kim Il Sung met his Chinese comrade Deng Xiaoping and told him North Korea had "already succeeded" in producing vinalon to ease the country's clothing problem. Deng said the process demanded electricity. But Kim was not worried.
"We won't need to use electricity in future. We can use oxygen," Kim said.
THE PEOPLE'S ECONOMY
In the early 1960s, as an anti-Communist coup in South Korea and the Cuban missile crisis sent North Korea down a path of military buildup, the economy was growing fast.
An economist at Cambridge University in England, Joan Robinson, visited in 1964 and wrote that "all the economic miracles of the postwar world are put into the shade" by what she saw, including vinalon. She recorded the formula for making it.
The North grew faster than the South - a trend which continued into the 1970s, according to UN and CIA economic data.
In 1972, the CIA recorded figures from 1956-1971 which showed the North had produced 7 million more metres of textiles than the South. In the early years the North's output of fish products, coal, iron ore, steel, cement, chemical fertilisers and tractors also exceeded that of the South.
The CIA figures show that until the mid 1960s, the North consistently exported more than the South in dollar terms.
KING OF FIBRES
North Koreans called vinalon "the King of Fibres" and featured it in cartoons to teach children how independent and successful the country was.
A TV show from 1976 shows Vinalon Man win a race against Mr Nylon.
But in reality, the fabric's limits were emerging. It was not good at keeping people warm. And power was becoming a problem. By now, oil was cheap in the West and the outside world was using it in abundance for energy, transportation and synthetic materials.
North Korea had no oil reserves for making vinalon or powering its factories and Pyongyang depended on oil imports from the Soviet Union. Even so, Kim Il Sung said North Korea must be independent.
"It may be cheaper and faster to produce the synthetic fibre using petro-chemistry ... But, constructing industries dependent on other countries' raw materials is the same as having others grab you by the collar," he said.
To help make its fabric of stone, the North wanted nuclear power. For years, it asked its Soviet allies to help with generation facilities. It only secured one nuclear power station. In 1967, vinalon inventor Ri was made head of the Atomic Energy Research Institute in Yongbyon. Today, this houses the North's light water nuclear reactor.
In 1973, Kim Dong Gyu, a high-ranking North Korean official, told Romania's leader Nicolai Ceaucescu that North Korea was producing "70-80 tons" of vinalon, and finding that hard to increase.
"Presently we are struggling to increase production in vinalon factories up to 50,000 tons per year," he said.
The Hamhung facility was expanded so it could make more calcium carbide, the coal and limestone compound on which vinalon is based. Soviet economies were driven by targets laid down in plans rather than the laws of supply and demand.
Calcium carbide can be used to make many things. Defectors from Hamhung told Reuters that it was thought to make chemical weapons - a claim others have also made and which is technically possible, but which no one has proven.
More recently, Western arms experts at the Middlebury Institute of International Studies suggested the vinalon plant might be used to help produce rocket fuel for missile tests. Scientists say this too is technically possible, but unproven.
As North Korea built up its military, its debts increased. It eventually owed a total of $11 billion to Moscow, most of which Russia was to write off in 2012. The North also accumulated debts in the West. They went unpaid year after year, totalling around $770 million in the 1970s.
Soviet support was declining, and China's new leader Deng Xiaoping was introducing market principles. He signed agreements on trade with North Korea in 1982.
North Korea started building a second vinalon factory in Sunchon in 1983, to achieve "a target 1.5 billion meters of cloth."
The factory was to be the biggest chemical industrial complex in the country and be controlled by the military. Kim's talk of running it on oxygen never materialised. Despite the reported $10 billion investment, the complex was never fully completed.
When the Soviet Union collapsed in 1991, North Korea lost all its Soviet funding. Chinese imports entered ordinary North Koreans' lives. China has exported hundreds of thousands of tons of textiles and clothing to North Korea, customs data show.
"In the 1990s, North Koreans relied mostly on Chinese fabric for their clothes. Since then, enormous amounts of Chinese fabric have been imported into North Korea," said Choi Goog-jin, a South Korean entrepreneur who tried to import North Korean vinalon in 2011.
CAPITALISM AT NIGHT
On July 8, 1994, Kim Il Sung died from a heart attack. His son Kim Jong Il took over, but within a year, Pyongyang was forced to ask international humanitarian agencies for aid.
Hamhung was hit by a flood and received no coal. It suspended fibre production.
There was no work. Residents from Hamhung said vinalon became the basis of an exchange scheme to survive. It was a similar story across the country.
Famine killed as many as 3 million North Koreans. North Koreans still call those years the "Arduous March," a term introduced by the official media to stir the starving.
Defectors say people took machine parts, as well as pure nickel and copper from wires and pipes, to informal markets.
By 1996, when vinalon's inventor Ri Sung Gi died, even party cadres loyal to the socialist system had turned to trading - a form of capitalist "self-reliance."
In 2001, Choi Goog-jin, the South Korean entrepreneur, created a company, Korea Vinylon Co Ltd, to import North Korean vinalon. After one year of sample tests and negotiations, the business failed.
In 2002, in Onsong County, North Korea, a high school student also called Choi said he bought a fake Adidas t-shirt and short pants from a market. The blue clothes were made of vinalon.
In 2010, Kim Jong Il reopened the February 8 Vinalon Complex.
"This is an extra-big event, as important as launching a new type A-bomb, and represents a great victory of socialism," he said.
The next year, he died suddenly on his private train. His son, Kim Jong Un, took over and in 2012 introduced economic changes, including turning a blind eye to the informal markets.
There was demand for vinalon - in those private markets.
Jung Min-woo, 29, served as a military officer before leaving North Korea in 2013. He said some ranking military officers bought custom-made shiny vinalon uniforms from private markets to look cool.
"Many ranking officers wear them... but they are not good for a war," he said.
"If war breaks out lots of sparks and bullets go back and forth... Cotton tends to melt and vanish but vinalon burns you because it sticks to your skin," Jung said.
By now, instead of producing vinalon, many North Koreans made clothes for China. Kang Eung Chan, who defected in 2013, said he hired 40 local seamstresses and used imported fabrics - including nylon - to make jumpers for Chinese customers. He paid locals $40-50 a month.
"Who wears vinalon now? Almost no one," said Kang.
Even so, North Korea says it still produces the fibre. In his 2017 New Year's speech, Kim Jong Un laid out a plan to revamp the vinalon complex.
If the new leader manages to drive North Korea's vinalon output with as much vigour as its missile tests, the fabric made of stone may yet find a new lease of life.
