The Birkenstock index is soaring, a measure of the anxious times we live in

During the first lockdown, some people bought campervans. Others got outdoor meat smokers. My lockdown impulse buy was a pair of black shearling Birkenstocks for €180. Even in those nightmarish, claustrophobic days, when you could get the Freedom of Dublin if you reported on enough neighbours for hosting an illegal barbecue party, I recognised this was insanely expensive for what are, essentially, ugly orthopaedic clogs.

Of course, as any Birkenstock wearer will tell you – likely at great length – these are not mere slippers with notions of high fashion and a much-vaunted cork sole. (Birkenstock prefers the term “footbed”. I like the Financial Times’s description: “the texture of an unappealingly dry quinoa salad”.) To fans, they’re an aesthetic, if not an entire lifestyle.

What they really are is a symptom.

Fans are enthused about their practicality, but that also has its limits. They’re not designed for running for the bus

Wearers insist their aesthetic shortcomings are more than compensated for by comfort. This much is undeniable. They are comfortable, at least once you’ve broken them in. And at a time when Starbucks makes you choose from 10 types of milk in your coffee and you can select from nine sexual orientations on Tinder, part of Birkenstocks’ appeal is a lack of choice. You can make slight modifications – hard or soft sole, with socks (please don’t) or without, and so on – but Birkenstocks are not about individuality.

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Fans are enthused about their practicality, but that also has its limits. They’re not designed for running for the bus. You can’t really wear them in the rain. They’re meant to make you feel like you’re “standing in sand”, but you should not stand on sand in them.

The secret of their appeal is that these are anxious times and to their core demographic of millennial and gen Z buyers, they seem to represent stability, predictability and timelessness. And so, between 2014 and 2019, sales of Birkenstocks increased by a steady 150 per cent. By 2020, revenues were €842 million. What happened next – lockdowns, working from home, social lives reduced to family quiz nights over Zoom and a corresponding rise in anxiety among the young – was a boon for the sensible German shoe-slipper hybrid.

Surrounded by uncertainty, many of us seem to have the impulse to dress like bean-eating, off-duty healthcare workers

The hemline index – an idea mooted by economist George Taylor in 1926, who claimed that skirts got longer as the economy slowed – is supposed to be a measure of economic confidence. Then chairman of Estée Lauder Leonard Lauder once suggested that when times are hard women are more likely to buy lipstick than pricy shoes, coining the term the lipstick index (his claim was, alas, not borne out by data following the 2008 crash).

But if there’s something in the idea that our behaviour and buying habits are reliable benchmarks of our mood, the Birkenstock index points to a troubled society. Surrounded by uncertainty, many of us seem to have the impulse to dress like off-duty healthcare workers.

Between 2020 and 2021, revenues at Birkenstock soared to €1.16 billion. Revenue in the six months to the end of March 2023 rose 19 per cent from the same period in the previous year.

Meanwhile, there were other cultural indicators that the shoe once primarily associated with a young Steve Jobs and plantar fasciitis sufferers had hit a tipping point: fashion house Valentino was one of several to launch its own high-end version. Barbie swapped stilettos for Birkenstocks when she embraced feminism in this summer’s hit cinema release.

And so there was an air of inevitability when Birkenstock this week announced plans to launch on the New York Stock Exchange, under the symbol Birk. Unnamed sources quoted in the Financial Times suggest a possible valuation of €7.4 billion.

Though Birkenstocks may strike the casual observer as shoes for sad times, that’s obviously not what they’re meant to signify. They are supposed to whisper quiet affluence and conscientious consumption. “Birkenstock is perceived as real – realness is an increasingly important success factor,” chief executive Oliver Reichert told the Financial Times in 2019.

It seems more than a bit ironic that while Birkenstock’s notion of authenticity is centred on its homespun image – the brand was founded in 1774, has been run by six generations of the same family and is still made in Germany

The Birk wearer wants you to know that they are a person who values substance over whatever the Kardashians are flogging on Instagram, but still has €150 to splurge on the latest release of Boston soft footbeds in faded khaki. Vogue magazine even has a name for this: the normcore aesthetic. (Along with normcore, another “key fashion trend” for this autumn and winter, or so the publication intones with all the gravitas of Christine Lagarde announcing the latest ECB rate rise, is “beige, in all its varying nuances.” A glorious time to be alive.)

During a time of war, pandemic, financial uncertainty, a housing crisis, fake news, a strengthening far-right, Instagram filters and AI, a shoe brand that pins itself to values like “realness” and “authenticity” is on to a winner.

In her book, Authenticity, Alice Sherwood unpicks the most over-used and meaningless of the terms of the internet age. “The promise of our age is authenticity as self-fulfilment,” she says. It’s not something we feel; it’s something we perform. We look for it in “our patterns of consumption, our job choices, how we relate to the world and its problems”.

It seems more than a bit ironic that while Birkenstock’s notion of authenticity is centred on its homespun image – the brand was founded in 1774, has been run by six generations of the same family and is still made in Germany – it has actually been owned since 2021 by a private equity firm, L Catterton, which acquired it after a takeover battle for €4 billion. L Catterton is part-owned by Louis Vuitton and Christian Dior owner LVMH. The €7.4 billion valuation suggested by the Financial Times would put Birkenstock at 18 times the forecasted Ebitda (earnings before interest, taxes, depreciation, and amortisation), placing it on a par with Nike.

In anxious times, manufacturing authenticity is big business.