The modern king of ultra-thin haute horlogerie, Bulgari has reworked its thinnest-ever Ultra watch from two years ago after Richard Mille took the crown of thinnest-ever mechanical watch. Reflecting its typical Swiss-Italian style, the new Bulgari Octo Finissimo Ultra COSC reclaims the title of the world’s thinnest mechanical watch and doubles down on it by becoming the thinnest COSC-certified chronometer watch, as well. It’s not only thin, but it also works and works well, claims Bulgari.

I distinctly remember the launch of the Bulgari Octo Finissimo Ultra in 2022 — now the 3rd thinnest watch in the world — and how all of us going hands-on with it asked Bulgari the same question: “Can… We… Pick it up? Yes? Then… Can we… Put it on?” The questions were raised because we all had vivid memories of recent encounters with other ultra-thin watches whose makers would not hand them over; they were so fragile in their thinness that only the respective brands’ watchmakers could handle them, with other members of the manufacture standing by, quietly sweating away in utter anxiety.

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By contrast, the Octo Finissimo Ultra we were all invited to put on. No, it’s not as robust as a regular Octo Finissimo, which in turn is not an indestructible thing either. That said, even this new, paper-thin Bulgari Octo Finissimo Ultra COSC watch that people are invited to wear. “If you can’t wear it, it’s not a watch,” says Bulgari.

How thin is it? The Bulgari Octo Finissimo Ultra COSC watch is just 1.70mm thick, making it the thinnest mechanical watch in the world. Bulgari claims it also “introduces a novel standard in watchmaking” by having its 1.50mm thick BVL180 movement pass the official chronometer tests of COSC (Contrôle Officiel Suisse des Chronomètres) because, and this won’t be news to you if you have been around watchmaking for some time, the more complicated or complex luxury watches are rarely ever (read: basically never) put through any form of proper independent testing for their performance.

You can have one, two, three, or four tourbillons, chiming mechanisms, gazillion-year calendars, or ultra-thin constructions — just don’t expect them to fulfill their core functionality reliably and work as accurate timekeepers. This (sad) reality is why we at aBlogtoWatch tend to highlight and indeed celebrate those few highly complicated watches that do comply with the strict criteria of established and independent testing. Chopard’s COSC-certified Full Strike minute repeater comes to mind as another high-performer.

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To shave another 0.1 mm off the 2022 Octo Finissimo Ultra, Bulgari reworked the sapphire crystal — apparently, it had another tenth of a millimeter in it, allowing Bulgari to show it to Richard Mille who had pushed the first Ultra off its throne after just a couple of months. It’s worth stopping here for a moment to think about that: just one-tenth of a millimeter. Over the years, it has happened at times when I realized I was getting lost in the significance of millimeters (let alone a few tenths of those) that I pictured a ruler, its centimeter scale, and how it is split into 10 fractions, each so small that their respective lines are almost touching… And then I’d try to imagine pointing at the amount I was writing about. Call me basic, if you want, but this practice has helped me realize the scale (or lack thereof) I was talking about.

From the moment you lift the new Octo Finissimo Ultra off the table, it feels like no other watch: It isn’t as light as you’d expect, since it is a relatively large watch head reinforced by a “particularly dense, hard, and ultra-resistant” tungsten carbide caseback that also serves as the mainplate of the movement. Having a separate caseback and mainplate is out of the question on a sub-2mm thick watch, but the rest of the exterior on the new Octo Finissimo Ultra COSC is either titanium or, get this, platinum. This time we went hands-on with the titanium version. When assessing its weight and feel, we also had to adjust our senses a bit since Bulgari certainly didn’t cheap out when it came to putting extra links into the bracelet, and the weight thus added does offset the overall feel of the watch.

Strangely enough, the 40mm wide case of the Bulgari Octo Finissimo Ultra COSC watch feels robust enough on the wrist. It is very wide — it’s worth noting that diameter measurements work very differently on square watches, so a 40mm wide watch with a square case tends to wear as large as a 42mm or even 44mm wide watch. The Ultra, then, has a wide stance on the wrist, with a bracelet to match, lending it the wearing experience of a wide ribbon of a watch rather than something fragile and filigree.

Rotate your arm, though, and the magic quickly reveals itself: the Octo Finissimo Ultra is, as you’d expect, breathtakingly thin. It looks more like an optical illusion than an actual watch, and we found ourselves adjusting it and touching it just to reassure our senses that it is indeed a real thing, and its case profile truly is as thick as a credit card — with the downturned lugs included, so the full thickness is apparently as thick as two cards.

Here are some other tricks of the Octo Finissimo Ultra COSC to achieve its record thinness beyond the caseback-mainplate combination. Developed together with Concepto, every moving part of the BVL180 caliber is spread out horizontally with as little overlap as possible, as parts arranged vertically add thickness. In alignment with this approach, the time display is split into hours (above) and minutes (below) subdials, while the running seconds — a requirement for COSC chronometer certification — is on a rotating satin-finished steel disc between the minutes and the balance wheel.

The mainspring barrel cover ditches the QR code from the previous version in favor of a miniaturized data matrix on the back, “it provides all the data relating to the watch and invites you on a personal journey into the Bulgari universe. With images and videos, it provides a better understanding of the quest for the ultimate finesse, the special skills and ingenuity that went into the creation of the Octo Finissimo Ultra COSC,” claims the brand.

The caseback reveals another secret: The two basic functions of a watch crown  — winding and setting — have also been separated so as to remove certain parts of the so-called keyless works that allows a regular crown to switch between those two or more functions. The larger wheel is used to wind the massive mainspring and replenish the 50-hour power reserve — quite something for an ultra-thin watch running at 4Hz frequency — while the smaller one sets the time. You can also see the tungsten carbide caseback, but bear in mind that a prototype piece was photographed here.

Then there is the folding clasp, that quite literally folds into the bracelet. The bracelet is fully openworked in large, rectangular areas, and the clasp folds into these spaces — had it been a regular clasp, the Octo Finissimo Ultra would have been many times thicker under the wrist than over it. This approach is also used on the “regular” Octo Finissimo, although that uses cavities rather than completely open spaces. It is a brilliant solution that many other bracelet-equipped watches would benefit from.

My favorite picture of the Bulgari Octo Finissimo Ultra COSC watch is the one above because with it I think I managed to capture just how incredible — and incredibly thin — it is. That’s a wristwatch, covered by a thin piece of paper. Now, to imagine how this watch would feel in platinum… Maybe we will get to report on that piece, with blue dials, someday.

The Bulgari Octo Finissimo Ultra COSC watch is available as a limited edition of 20 pieces in titanium (reference 104081) and 20 pieces in platinum (reference 103832). The Bulgari Octo Finissimo Ultra COSC watch is priced at $529,000 USD in titanium and $546,000 USD in platinum. You can learn more at the brand’s website.

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