The short answer
Waon (和温) therapy — the characters mean "soothing warmth" — is a Japanese practice developed from the late 1980s by Dr Chuwa Tei, a cardiologist at Kagoshima University. The protocol is simple: fifteen minutes in a far-infrared dry sauna set to a mild 60°C, which raises core temperature by about one degree, followed by thirty minutes of rest wrapped in blankets to hold that warmth. Tei studied it for decades in Japanese hospitals, mostly in people with heart conditions, and it is now part of Japan's health-insurance system for certain patients. The lesson that travels beyond the hospital is the temperature: sixty degrees, not ninety. Warm, not hot.
Why "warm" rather than "hot"
A Finnish sauna runs at 80 to 100°C. Waon runs at 60. The difference is not a compromise; it is the point. At sixty degrees the body warms through without going into defence — no racing heart, no gasping, no sense of being cooked. Blood vessels open gently. The core rises by a degree and stays there through the rest period. Tei's argument, made in paper after paper, was that this gentle, sustained warmth relaxes the vessels and eases the load on the heart in a way that intense heat, which the body treats as a stressor, does not.
Anyone who has been in a too-hot bath knows the difference in their body before they know it in their head. Hot is something you endure. Warm is something you sink into.
Why "whole body" and why "repeated"
Two other features of Waon matter. It warms the whole body evenly, not one patch. And it is done daily, or near it, for weeks. The benefit Tei measured came from accumulation, not from a single dramatic session. This is the opposite of how most of us use warmth in the West — a sauna on holiday, a bath when we are ill, a hot-water bottle when the flat is freezing. Warmth as an event. Waon treats it as a practice.
The rest is not optional
The thirty minutes under blankets is half the protocol. The sauna raises the temperature; the rest keeps it there long enough to matter. Skip the rest and you have had a warm quarter of an hour. Keep it and the body is given time to do what it does when it is warm and unbothered: soften, slow down, let go.
What we take from it — and what we don't
Kozy is not a medical company and Litual is not a treatment. We are not going to tell you that a bed topper does what a hospital sauna does. What we took from Waon is a set of design decisions, and we are open about them.
Mild over hot. Litual's warmth is meant to be sunk into, not endured. The first-night setting we suggest is 27°C, and most people go lower from there, not higher.
Whole body. A topper under the fitted sheet warms the length of you, not a patch.
Every night, not once a week. The one ritual nobody skips is going to bed. Warmth built into that ritual happens daily by default, without you having to remember or decide.
Rest is the point. Waon ends in thirty minutes of lying still under blankets. Litual starts there. The whole night is the rest period.
A note on Korea
None of this would surprise a Korean grandmother. Korean culture has treated warmth as a daily practice for three thousand years — floors heated from underneath, postpartum weeks spent warm and resting, the reflexive instinct to press a tired back against a hot floor. Japan measured it; Korea lived it. We are trying to bring both to a bed in Paris, or Munich, or wherever you are reading this.
Questions people ask
What temperature is Waon therapy?
The sauna is set to about 60°C — deliberately mild compared with a traditional Finnish sauna at 80 to 100°C. The session is around fifteen minutes, followed by thirty minutes of rest under blankets.
Is Waon therapy the same as an infrared sauna?
It uses a far-infrared dry sauna, but the defining features are the mild temperature, the rest period and the repetition, not the sauna itself.
Does Litual do what Waon therapy does?
No. Litual is a bedding product, not a medical device, and we make no medical claims for it. What it shares with Waon is a philosophy: mild, whole-body, repeated warmth followed by rest.
Can I try warmth practices if I have a heart condition?
Talk to your doctor first. Waon therapy is administered in hospitals under supervision for a reason, and any warming practice — including a heated bed — should be discussed with a clinician if you have a cardiovascular condition or reduced sensitivity to heat.
This piece describes a Japanese medical practice for context. It is not medical advice, and Kozy products are not medical devices.