What exactly does "se mettre sur son 31" means ?

Even though society evolves, times change, and habits transform, one tradition remains deeply rooted, clinging like a mussel to a rock in French end-of-year holiday culture: se mettre sur son 31 (literally "to put on you 31rd", dressing to the nines in english). Barely finished with the series of Christmas meals and before even digesting the yule log, the glitter is back, and it's time to start again. Woe to anyone who dares show up to their New Year’s Eve party in a normcore outfit without pulling out the bow tie, in an ironic, almost caricature-like contrast of a generation today struggling with injunctions. While this expression, commonly meaning “dressing up,” “wearing your finest clothes,” or “making an effort to look elegant,” is automatically associated with December 31st, its origins actually date back to the Middle Ages. 

Indeed, we owe the expression to a specific fabric used during the Middle Ages when someone wanted to stand out and be noticed: the trentain. The warp of this luxurious fabric was composed of thirty times one hundred threads, mistakenly transformed into “trente et un” (thirty-one), which later became trentain. The phrase “se mettre sur son trente et un” literally means “putting on your trentain”, which by extension, signifies wearing your finest adornments. However, today, dressing to the nines is no longer limited to elegant clothing but encompasses a shift in attitude and energy, embodying the idea of boosting confidence without fear of being seen and shining brightly. “What’s fascinating is that today’s youth is doing the exact opposite of the youth in the 1970s. In 1970, one would rather die than wear a tie. The fight was to avoid looking like those already-old 20-year-old men of the 1960s,” explains Sophie Fontanel in her article for Harper’s Bazaar.

With the continuous return of past trends and, especially, the success of vintage in 2024, slicking back hair with gel, putting on your finest loafers, and adorning yourself with your most eccentric family jewels has never been trendier. Pulling out your best attire to welcome the New Year therefore embodies luxury in its purest form: stepping into the new year with head held high and looking your best, taking that first step into the future in the best possible way to attract abundance, self-confidence, and well-being, while feeling part of a group since, of course, you won’t be the only one sporting a glittery dress and a boa. While it may seem hard to believe in a world dictated by micro-trends and subtle yet pervasive marketing, it is neither the latter nor consumerism that tells us how to dress on December 31st but culture itself. If, by 2024 and likely in 2025 as well, we’ve already understood that clothes make (or at least attempt to make) the man, a little sparkle in our lives to kick off 2025 can’t be a bad omen.