Carbon fiber

Carbon fiber is not a single material: it's a family. From the workbench, I've learned that confusing laminated carbon, forged carbon, and hybrid composites is the most common mistake, even among people who've been selling watches for years.

The basic process is always the same: carbon filaments — diameter around 5–10 micrometers — are impregnated with epoxy resin, arranged in a mold, heated at high temperature, and compressed at high pressure. The result is a material with a rigidity-to-weight ratio that steel cannot match. But it's the orientation of the fibers that determines everything else.

In unidirectional carbon, the fibers run parallel in a single direction: maximum axial rigidity, regular striped pattern. In forged carbon — a term popularized by Lamborghini before it arrived in watchmaking — the filaments are cut short and oriented randomly in the mold. The visual effect is marbled, not mesh weave, and each piece is different from the next. It's this surface uniqueness that made forged carbon attractive to manufacturers wanting to differentiate themselves from the 2000s aesthetic of twill carbon.

Then there are hybrid composites, and here the variety has become almost impossible to follow without a dedicated archive. Norqain developed Norteq, a composite with a 60% bio-based polymer matrix derived from castor oil: six times lighter than steel. Hermès infused graphene powder into the fiber for the H08, achieving a granular texture to the touch along with improved mechanical properties. Behrens deposited a diamond coating on carbon fiber — called SPSCF — to combine surface hardness with minimal weight. Hublot layered a sheet of Texalium, fiberglass with an aluminum surface, over carbon cases to increase scratch resistance. Bulgari combined rose gold and carbon fiber in a single structural material called CarbonGold, with roots dating back to 1993.

A clarification I often make: black PVD on brushed steel can visually imitate the appearance of carbon, but it has nothing in common structurally. It retains steel's weight and thermal conductivity. Anyone buying thinking they have carbon on their wrist notices the difference at the first weighing.

A technical detail I find interesting, though I have no direct experience applying it in watchmaking: HealTech technology provides for the carbon surface to self-repair when heated between 100 and 150°C. In aerospace, it's already operational. In watchmaking it has been announced but I have not verified actual implementations in series production.