When actress Margot Robbie swapped high heels for pink Birkenstocks in hit summer movie "Barbie", it illustrated how the sandals have transformed from unglamorous, practical footwear to a highly-coveted fashion item.

The company was founded 250 years ago in rural Germany, and remained in the hands of the Birkenstock family until heirs, brothers Alex and Christian, sold a majority stake in 2021.

The footwear brand announced Tuesday it was preparing to take another step into the big leagues with an IPO in New York, which could reportedly value the company at over $8 billion (7.4 billion euros).

Here are five things to know about Birkenstock:

– From a German village to the big time –

The company traces its roots back to 1774 and Johann Adam Birkenstock, who worked as a cobbler in Langen-Bergheim, a small community in western Germany.

In 1896, Konrad Birkenstock began focusing on orthopedic footwear, developing comfortable, contoured insoles designed to cushion the feet.

The sandals rose to international prominence when they arrived in the United States in the 1960s, where they were adopted by hippies who saw their no-frills look as an anti-fashion badge.

But they really shed their association with sock-and-sandal-wearing Germans and became a trendy, must-have item in the 1990s, when supermodel Kate Moss donned a pair for a fashion shoot.

The company remained in the hands of the founding family until 2021 when the Birkenstock brothers sold a majority stake.

It was snapped up by LVMH-linked equity firm L Catterton and French billionaire Bernard Arnault's family holding fund Financiere Agache, for a reported sum of around four billion euros.

The Birkenstock brothers have retained a minority stake.

– From Arizona to Madrid –

Birkenstock's most famous sandal is the Arizona, which features two wide straps with buckles, on trademark cork and latex soles.

Introduced in 1973, they became a symbol of US counter-culture and, while they are available in different colors and material, the shoe's basic design has not changed.

The single-strap Madrid, introduced a decade before the Arizona, helped lay the foundation for the company's later successes, and was originally known as "the gymnastics sandal" as it exercises a wearer's foot and leg muscles as they walk.

Other models include a thong sandal, Gizeh, which takes its name from an Egyptian city, in a nod to sandals' centuries-old history.

There are a range of variations on the original models, such as sandals with platforms and water-proof versions, and Birkenstock makes other shoes, from clogs to trainers.

While the company has mainly stuck to making shoes, they have branched into other products, including high-end beds and skin care products.

The shoes are, however, not cheap, with prices reaching up to 230 euros ($247) for the most elaborate models.

– 'Made (mostly) in Germany' –

While other companies have shifted production to places where labor is generally cheaper, such as Asia, Birkenstock says 95 percent of its products are assembled in Germany.

Headquartered in the picturesque city of Linz am Rhein in western Germany, the company has several manufacturing sites in the country, and around 6,200 employees worldwide.

Its newest factory near Pasewalk, in the eastern state of Mecklenburg-Western Pommerania, started production earlier this month.

– Beloved by VIPs –

Margot Robbie was just the latest celebrity to be seen sporting a pair of now ultra-trendy Birkenstocks. A parade of Hollywood A-listers and pop stars have donned the sandals in recent years, often opting for Arizonas, from singers Katy Perry and Britney Spears to actress Katie Holmes.

Birkenstock has also launched tie-ups with fashion brands, including Paco Rabanne, Valentino and Celine, which have customized their own versions.

– Sustainability –

Birkenstock says the protection of natural resources is at the heart of its products. The company uses materials from sustainable sources, such as cork, natural latex, jute and leather.

It also offers vegan sandals, manufactured solely with plant-based and synthetic materials.

Cork — a key material in Birkenstock insoles — is also central to the company's cosmetics. Cork oak extract, said to possess anti-ageing properties, is a main ingredient in Birkenstock's skin care products.

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© Agence France-Presse