What Is WBGT (Wet Bulb Globe Temperature)?
WBGT, or Wet Bulb Globe Temperature, is a heat stress index that combines natural wet bulb temperature (evaporative cooling), globe temperature (radiant heat), and — outdoors — dry bulb air temperature into one value used to assess heat strain risk. Because evaporation is the body's primary cooling mechanism, natural wet bulb temperature drives 70% of the WBGT value, indoors and outdoors alike.
Indoors and Outdoors
Natural Wet Bulb Drives 70% of WBGT
The two WBGT equations below show how the index is built. In both cases, natural wet bulb temperature carries the largest weight, which is why measuring it accurately — including the wind or airflow that drives evaporation — matters more than any other input.
Why Waterless Is Better
No Wick. No Water. No Maintenance.
Traditional WBGT sensors rely on a wetted wick that must be prepared and maintained. Modern instruments can model natural wet bulb temperature without water using validated heat-transfer equations — provided they measure the correct environmental inputs, including wind speed or airflow. Kestrel's waterless WBGT requires no setup and no consumables, reducing user error and ensuring consistent, accurate measurements every time.
Wetted Wick
- Requires manual wetting before every use
- Can dry out mid-shift, invalidating readings
- Sensitive to dust, salt, and contamination
- Requires ongoing maintenance and wick replacement
Kestrel Waterless WBGT
- No wick preparation, ever
- No maintenance or replacement parts
- Consistent measurements across users and shifts
- Immediate deployment — power on and go
Why it Works
Evaporative Cooling Depends on Airflow
Higher wind or airflow means more evaporative heat exchange; lower wind or airflow means more heat retention. A device that isn't measuring wind or airflow is missing a key input to the evaporative cooling calculation that drives 70% of WBGT — which is exactly why Kestrel builds wind and airflow measurement directly into every waterless WBGT reading.
Outdoors: Wind
Open-air wind speed increases evaporative cooling from sweat and drives the natural wet bulb calculation used in outdoor WBGT.
Indoors: Airflow
Indoor airflow from HVAC, fans, or ventilation plays the same evaporative-cooling role that open-air wind plays outdoors — and indoor WBGT also accounts for radiant heat from equipment, machinery, floors, and walls via the globe temperature measurement.