Marketing copy treats them as interchangeable. They aren't. A traditional Finnish sauna and an infrared cabin produce a different stress response, target different tissue depths, and have very different research backings. Here's the practical breakdown.
How they actually heat you
Finnish (convective): hot rocks heat the air to 80–110°C. Your body warms primarily through air contact and radiative transfer from the heated wood and stones. You sweat heavily within 5–10 minutes. Humidity can be raised by pouring water on the rocks (löyly), pushing perceived heat much higher.
Infrared (radiant): emitters output IR-A, IR-B, or far-infrared wavelengths that pass through air and are absorbed by skin. Air temperature stays at 45–65°C. Sweating starts later — often 15–20 minutes in — but persists at lower ambient heat.
The physiological cost
| Metric | Finnish 90°C | Infrared 60°C |
|---|---|---|
| Peak heart rate | 120–150 bpm | 95–115 bpm |
| Core temp rise | +0.8 to +1.2°C | +0.3 to +0.7°C |
| Sweat rate | High, fast | Moderate, sustained |
| HSP72 expression | Strong, well-documented | Modest, less data |
| Tolerance for first-timers | Hard | Easy |
What the research backs each for
Finnish sauna has the deeper bench: decades of Finnish cohort data on cardiovascular and all-cause mortality, plus shorter trials showing improvements in arterial stiffness, blood pressure, and exercise capacity. If your goal is the cardiovascular conditioning effect, this is the heat source with the evidence.
Infrared has a thinner but real evidence base for muscle recovery, perceived pain reduction, and sleep onset improvements. Its lower cardiovascular load makes it accessible for people who can't tolerate 90°C — older users, beginners, anyone deconditioned.
If you want adaptation, go Finnish. If you want recovery, infrared earns its place.
Picking by goal
- Cardiovascular adaptation, longevity: Finnish, 80–100°C, 4×/week.
- Heat acclimation for endurance sport: Finnish, 85–95°C, daily for 7–10 days then taper.
- Recovery between hard training days: Either works. Infrared if you're already fatigued.
- Sleep onset, parasympathetic shift: Either, but timed 90 minutes before bed.
- Beginners: Infrared at 55°C for 20 minutes builds tolerance before stepping up.
What Sauna Metrics does with the difference
The app's scoring system bands temperature differently for each type. A 60°C infrared session isn't penalized for being "too cold" — it's scored against the infrared evidence base. A 90°C Finnish session is scored against the Kuopio range. You log the type once, the math adjusts.
The physiology is different. The score should be too.