Fire-Dex Blog

How Turnout Breathability Affects Firefighter Heat Stress

Turnout Breathability & Heat Stress

As a firefighter, you're more exposed to heat stress than the general public. To reduce this risk, your body self-regulates its core temperature through evaporation of sweat. Suiting up in turnouts can hinder this process so it's vital that your sweat has an exit to escape. 

Get the facts about how your body keeps cool: 

  • Sweat - the body's natural response helps carry heat away from its core 💦
  • Core Regulation - when sweat evaporates, core temp can self-regulate 🌡️
  • Wicking - pulls sweat away from the skin to keep you dry ⬆️
  • Breathability - materials must allow the moisture vapor to escape 💨

Choosing breathable turnout composites that support this natural cooling process will allow for proper evaporation to occur. That's why we design custom turnouts to minimize heat stress and fatigue, built to give you elite protection with the highest quality materials! 


Sweat Test: The Role Turnouts Play in Firefighter Heat Stress

Sweat evaporation is critical for cooling the body and breathability makes a huge difference! Learn more about how Ret and THL are both great indicators of breathability performance: 

What is THL?

Total Heat Loss (THL), measures breathability or the ability of the total composite system to allow heat and moisture to evaporate. 20 years ago, this test was formulated by the fire service to measure breathability, a key factor in reducing heat stress. 

  • Provides a good way to compare materials in relatively mild environmental conditions 
  • The THL average of all the certified composites in the current NFPA 1971 standard is 248.4 
  • The higher the value = better breathability score

What is Ret?

Resistance to Evaporative Heat Loss (Ret) assesses how well your clothing effectively allows for evaporative cooling. Whether you're responding to it’s an MVA or fully involved structure fire, you sweat. Your turnout gear needs to be able to remove the perspiration through the garment and evaporate, just like any athletic performance wear. If you can’t evaporate your sweat, it can lead to your body overheating and increase cardiac stress. 

  • Ret directly measures how quickly a 3 layer composite system allows moisture to escape 
  • Ret is used within the fire service in Europe (EN469) and throughout the U.S. in performance apparel
  • Provides stronger insight into turnout breathability performance in warmer environments
  • Less resistance = better breathability  


So, how do our composites compare? Our composites are the lightest, thinnest, most breathable, and flexible in the fire service! Check out the stats in the chart below. 🔥



With the leading Ret and THL numbers in the industry, Request A Quote to upgrade your gear today! 👇



Categorized: Firefighter Health and Safety, Heat Stress and Cardiac Strain, THL, TECGEN71, RET


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