Reference
Sauna and cold plunge glossary
The terms that show up in product specifications, defined in plain language, with what each one actually changes when you are choosing between products.
23 terms · Reviewed 2026-08-15
Most confusion in this category comes from a handful of terms doing double duty. Horsepower describes a compressor, not cooling delivered. A material's temperature tolerance is not a temperature the system can reach. Full spectrum is a marketing category, not a measurement. Each definition below says what the term means and what it changes for a buyer.
Heat
LöylyLöyly is the burst of steam produced when water is ladled onto hot sauna stones, and the wave of moist heat that follows.Far infraredFar infrared is the longest-wavelength band of infrared radiation, roughly 3 to 1000 micrometres.Full spectrum infraredA full-spectrum infrared sauna uses emitters covering near, mid and far infrared rather than far infrared alone.EMFEMF stands for electromagnetic field, the field produced by any electrical device including a sauna heater.ThermowoodThermowood is timber that has been heat-treated at around 400°F in a low-oxygen kiln, without chemicals.Sauna blanketA sauna blanket is a padded, zip-up envelope with far-infrared heating elements built into its lining.
Cold
Systems
Heater sizingSauna heaters are rated in kilowatts, and the rating must match the room's volume.240V hard-wireA hard-wired circuit is connected permanently to the electrical panel rather than plugged into an outlet.Water chillerA water chiller is a refrigeration unit that pumps water out of the plunge, cools it through a heat exchanger, and returns it.BTU per hourBTU per hour measures how much heat a chiller can remove in an hour.Chiller horsepowerHorsepower describes the compressor in a chiller, not the cooling delivered.Cooling rateCooling rate is how fast a chiller lowers water temperature, usually published in degrees Fahrenheit per hour.Ozone sanitationAn ozone generator produces O₃ gas and injects it into the circulating water, where it oxidises bacteria and organic matter before reverting to ordinary oxygen.Micron ratingA filter's micron rating is the size of particle it captures, measured in millionths of a metre.Drop-stitch constructionDrop-stitch is an inflatable construction method where thousands of threads connect the inner and outer walls, holding them parallel under pressure.Filled weightFilled weight is the mass of the vessel plus its water, and it is far larger than most buyers expect.Ambient operating rangeAmbient operating range is the air temperature a chiller can work in, not the water temperature it can reach.Titanium heat exchangerThe heat exchanger is the coil where refrigerant draws heat out of the water, so it sits in constant contact with the water supply.
Evidence
Cold shock responseCold shock response is the involuntary reaction to sudden cold-water immersion: an initial gasp, rapid uncontrolled breathing, a spike in heart rate and blood pressure.Contrast therapyContrast therapy alternates heat and cold exposure in a single session, typically a sauna followed immediately by a cold plunge, sometimes repeated.Manufacturer claimOn SweatFreeze, a fact labelled 'manufacturer claim' is a figure the maker publishes that depends on conditions we cannot verify — a maximum temperature, a cooling rate, a preheat time.Not published'Not published' means the manufacturer does not state that figure anywhere we could find on their own site.