It’s always a fun day when something that purports to be unfashionable suddenly becomes fashionable. Today is that day and comfortable shoes are that thing.

This is remarkable for two reasons. Firstly, it marks an end to the ugly shoe’s two-year reign of terror. And secondly, since when did fashion care about comfort?

“It’s a dirty word, so we were warned off it,” says Tim Brown, co-founder of Allbirds, the incredibly sensible shoe company, which Time magazine called “the world’s most comfortable shoe”, and whose fabric one Google reviewer compared to “clouds”. The brand’s neat little woollen trainers, worn by the likes of Leonardo DiCaprio, Mila Kunis, and Emma Watson, are affordable, logo-free, environmentally friendly, and deeply uncool. They have also just sold their millionth pair.

For context, it’s worth remembering that 2018 was defined by the ugly trainer: bulbous, sometimes artfully distressed, ironic, anti-beauty and weird. Louis Vuitton, Prada and Gucci did them. So did Zara, Topshop and Fila. They were an in-joke – and an expensive one at that (Balenciaga’s Triple S trainers cost £645 and come a little dirtied), all rooted in Miuccia Prada’s logic that “ugly is attractive, ugly is exciting. The investigation of ugliness is, to me, more interesting than the bourgeois idea of beauty.” To get the joke, you were the joke.

Candy-pink Escada basketball sneakers worn at New York fashion week in 2018. Photograph: Pietro D’Aprano/FilmMagic

Still, by the end of 2018, ugly trainers had reached critical mass. Low points included Jimmy Choo’s Diamond trainers or the candy-pink Escada basketball sneakers. Not only were they the dominant footwear on both catwalk and high street, but you might not want to play basketball in them either.

By contrast, you can do anything in a pair of sensible trainers. Shoes that are unremarkable but functional, one colour and washable. Not exactly pretty, but an inversion of ugly trainers. Alongside Allbirds, see also Cole Haan’s Zerogrand trainer (so comfortable you can sleep in them, one imagines) and Camper’s Pelotas, an annual bestseller. Trainers themselves are going nowhere – in the past year or so, global sales of high heels dropped 12%, while sales of women’s sneakers rose 37% – but the sort of trainers we wear is shifting.

Allbirds launched in 2016 with a single pair of lace-ups, designed for men and women, which came in soft merino wool. They now have six styles and a UK shop. According to Brown, they benefitted from the “casualisation of fashion, which just hadn’t come to footwear”. They describe their anti-style as “the right amount of nothing”.

Unsurprisingly, they are most popular in Silicon Valley, where looking remarkable is frowned upon. Fans include Google’s Larry Page and the former Twitter chief Dick Costolo. Speaking from his San Francisco headquarters, Brown is unclear why they’re popular with tech types, but says that “San Francisco is struggling with its own identity, so maybe that’s why?” Silicon Valley’s biggest disruptor, whistleblower Christopher Wylie, wears fashion’s original ugly trainer – the Balenciaga Triple S in dove grey.

Their popularity makes cultural sense, if nothing else. Designed to be worn 24 hours a day and, in the case of Allbirds, without socks, these are trainers for the hygge generation, for whom cosiness is a mindset. They are also, arguably, Kondo-pleasingly neat. While the sensible shoe is not quite an act of civil dissent, this sort of protest is still two fingers up to an industry that thinks it can control the narrative. Even if comfy shoes represent their own kind of ugliness.