A Sauna Is More Than a Temperature

When people in the Philippines ask about a sauna, one of the first questions is usually simple:

How hot does it get?

Temperature matters. But in a Finnish sauna, it has never been the whole story.

Water is thrown onto hot stones to create löyly — the temporary increase in steam, heat and humidity that moves through the room. It is one of the defining characteristics of Finnish sauna bathing, and new research from Finland gives us a clearer picture of how significantly it changes the body's response.

A 2026 study published in the peer-reviewed journal Temperature examined 50 healthy adults across four 10-minute sauna sessions. The saunas were kept at approximately 75°C while researchers measured the conditions inside the room together with heart rate, skin temperature and core body temperature.

Humidity changes what the same temperature feels like

Across the sessions, participants' heart rates rose on average from approximately 79 to 121 beats per minute — an increase of 41.6 bpm. Average core temperature rose from around 37.4°C to 37.8°C.

Temperature was still the strongest influence, but humidity also had a measurable, independent effect. Higher relative humidity was associated with greater increases in heart rate and core body temperature.

The contrast between sessions was substantial. In the driest conditions, where participants did not throw water on the stones, relative humidity was around 6%. In sessions with the most löyly, it reached approximately 59%. Across those measured conditions, the difference in core-temperature response approached half a degree Celsius.

Two sauna rooms can show the same temperature on the thermometer and still provide very different experiences.

This is especially relevant in the Philippines

In the Philippines, sauna is sometimes treated primarily as a heating problem: choose a heater, calculate the room volume, reach the required temperature.

That is necessary, but it is not enough.

A Finnish sauna is designed around what happens after water is thrown onto the stones.

The heater needs to perform properly under repeated löyly. The stone mass and arrangement need to be appropriate. The benches have to position bathers correctly within the heat zone. Ventilation needs to bring in fresh air while allowing heat and löyly to circulate through the room. Glass, stone and other heat-loss surfaces all change the way the sauna behaves.

This is why we do not design around a maximum temperature alone.

Philippine humidity is not the same as löyly

There is also an important distinction in a tropical climate. The Philippines is already humid. But atmospheric humidity outside a sauna and löyly inside one are very different things.

Löyly is a short, controlled rise in humidity created when water meets properly heated sauna stones. It allows the bather to change the intensity and character of the sauna during the session.

A sauna that simply feels permanently damp because of poor ventilation is not achieving the same thing.

The objective is not maximum humidity. It is controlled heat, controlled löyly and a room that responds properly when the bather adds water.

What the study does — and does not — tell us

The researchers used four sauna setups with electric, wood-burning, gas and hydrogen heating, all operating at approximately the same target temperature. Humidity remained an independent factor in the physiological response across the measured sessions.

The study does not mean that more humidity is always better.

It also did not investigate long-term health outcomes. It measured immediate cardiovascular and thermoregulatory responses during sauna bathing.

What it does reinforce is a principle fundamental to Finnish sauna:

Heat and löyly work together.

The better question

Instead of asking only how hot the sauna will get, we prefer to ask how the room will behave when people actually use it.

• Can the bather throw water comfortably?
• Does the heater recover properly?
• Is the upper bench positioned in the right heat zone?
• Does fresh air reach the bathers?
• Does the löyly move through the room rather than disappearing immediately or becoming oppressive?

Those questions determine whether a sauna merely reaches a temperature or actually works as a Finnish sauna. That is what we design for — the same principles set out in our guide to the Finnish sauna.