What it does
The hairspring sits at the centre of the balance wheel, fixed at one end to the balance staff and at the other to a stud on the balance cock. It is a spiral spring, normally with 12 to 15 coils, that resists the balance's motion in both directions. Each time the balance swings out, the hairspring stores energy and releases it back into the swing. This is what gives the balance its natural period; it is also what makes the watch run fast or slow when the spring is upset.
Nivarox: the workhorse
Most Swiss mechanical watches you can buy in 2026 use a Nivarox hairspring. Developed in the 1930s by Reinhard Straumann, Nivarox is a nickel-iron-chromium alloy designed to be temperature-stable and somewhat anti-magnetic. It is graded from 1 to 5, with Nivarox 1 reserved for chronometer-grade movements. The same factory (Nivarox-FAR, owned by the Swatch Group) supplies hairsprings to most of the industry: ETA, Sellita, and a long list of brands. A Nivarox-equipped watch is fine in everyday wear but will gain or lose minutes if you bring it near a strong magnet.
Silicon: the modern leap
Silicon hairsprings entered serial production in 2001 with Ulysse Nardin's Freak, then spread through the industry. Silicon is completely non-magnetic, ten times lighter than steel, near-frictionless against air, and dimensionally stable across a wide temperature range. It is also brittle: drop the watch hard and you can shatter the hairspring (very rare in practice but uninsurable). Today silicon hairsprings appear in Patek (Spiromax), Omega Master Chronometer, Ulysse Nardin, and many independents. Rolex stuck with a metal alloy until the new Cal. 7140 (2024).
Parachrom (Rolex)
Parachrom Bleu is Rolex's in-house niobium-zirconium-oxygen alloy hairspring, introduced in 2000 in the Daytona's Cal. 4130. It is paramagnetic (not fully anti-magnetic but ten times less affected than Nivarox), highly resistant to shock, and visibly blue under bright light because of an oxide layer that forms during manufacturing. A Parachrom Bleu spring is a strong indicator that the watch is a 2005-or-later Rolex with an in-house chronograph or three-hand calibre. The newer Syloxi (silicon, in the Pearlmaster and now Cal. 7140) is Rolex's answer to the rest of the industry going silicon.
Spiromax & Pulsomax (Patek)
Patek Philippe introduced the Spiromax silicon hairspring in 2006 and now uses it across most of its mechanical catalogue. Spiromax has a patented terminal curve at the outer coil that gives near-perfect concentric breathing, which improves rate stability across all positions. Pulsomax is Patek's matching silicon escape wheel and lever, used in higher-tier calibres like the Cal. 240 PS IRM C LU. Together, Spiromax + Pulsomax give Patek a non-magnetic, low-friction escapement comparable to silicon-equipped Omegas and Ulysse Nardins, just with a different name and an in-house process.
What this means for buyers
Hairspring material is the single biggest predictor of how a modern watch behaves around magnets and temperature. Buying a daily wearer? A silicon or Parachrom-equipped watch will outperform a Nivarox watch in real life, especially around laptops, MRI machines, magnetic clasps, induction stoves, and speakers. Vintage buyers should know that any pre-2000 watch has a steel hairspring that can be magnetised; a CHF 50 demagnetiser is the cheapest "service" you can ever buy. For more on accuracy, see how accurate are mechanical watches.