--- title: The Turnout Gear Terms You Need to Know description: Why firefighters must understand TPP, THL, and Ret when evaluating turnout protection levels. image: https://blog.firedex.com/hubfs/Blog%20Banners-1.png --- - [ABOUT](https://www.firedex.com/about) - [About](https://www.firedex.com/about/) - [Meet the Team](https://www.firedex.com/about/meet-the-team) - [Employment](https://www.firedex.com/employment/) - [Now Hiring](https://www.firedex.com/employment/#hiringnow) - [Resources](https://www.firedex.com/education-resources/) - [Fire-Dex PPE Rentals](https://www.firedex.com/fire-dex-ppe-rentals/) - [NFPA Performance Requirements](https://www.firedex.com/education-resources/nfpa-performance-requirements/) - [Drag Rescue Device Installation Guide](https://www.firedex.com/drd-installment-guide/) - [Heat Stress E-Book](https://landingpage.firedex.com/ret-e-book) - [Blog](https://blog.firedex.com/blog) - [Shop Online](https://firedex.com/shop) - [My Account](https://firedex.com/my-account) - 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It’s the front line of defense for firefighters, with a significant impact on fireground safety and performance. Small decisions during the selection process can have a big impact on real-world performance.   That’s why it’s helpful to take turnouts down to their most basic parts to make comparisons easier.   At their core, turnouts are a three-layer garment designed to protect firefighters against the dangerous elements of the fireground. But [more](https://experts.illinois.edu/en/publications/firefighter-fatalities-and-injuries-the-role-of-heat-stress-and-p/) and [more](https://www.fsi.illinois.edu/documents/research/FFLSRC_FinalReport.pdf) research has shown that the [greatest danger to firefighters](https://www.nfpa.org/education-and-research/research/nfpa-research/fire-statistical-reports/fatal-firefighter-injuries) on the fireground is [overexertion](https://blog.firedex.com/blog/what-firefighters-need-to-know-about-heart-health) and [heat stress](https://landingpage.firedex.com/ret-e-book).  That’s why PPE guidelines require manufacturers to share information about not only how well turnouts protect from heat, but also how well they protect from heat stress.   To understand what those numbers mean, firefighters must know the makeup of their gear (the composite) and the importance of TPP, THL, and Ret.   ### **A Guide to Turnout Materials**  Today’s turnout gear is built using a three-layer system, usually just called “the composite.” Fire departments can choose composites based on their goals, such as budget, the types of calls they receive most often, and what’s worked in the past.   Each layer plays a unique role in protecting firefighters on the job.  #### **1. Outer Shell** This is the gear’s first line of defense. It’s made from flame-resistant materials that also stand up to cuts, scrapes, and general wear and tear. Outer shells materials are made to resist water and oil absorption, offering an extra layer of moisture protection.  Depending on the material, outer shells vary widely in terms of weight, breathability, durability, and even color options.  #### **2. Moisture Barrier** Next comes the moisture barrier. This middle layer keeps out water, chemicals, and bloodborne pathogens.  To meet NFPA standards, gear must pass a “shower test,” where it’s sprayed with water to ensure nothing leaks through. Together, the outer shell and moisture barrier work to keep harmful moisture out.  But it’s not just about keeping water out, it’s also about letting sweat escape. If sweat gets trapped inside the gear, it can lead to heat stress and other health risks. That’s why moisture barriers are designed to block external moisture while still allowing internal vapor to escape.  #### **3. Thermal Liner** Closest to the body is the thermal liner. This layer insulates the firefighter from extreme heat and is usually made from quilted or laminated fabrics. It’s the last line of defense against burns and plays a major role in how protective the gear is overall. Like the other layers, it’s tested to ensure it can handle high temperatures. ### **How to Choose a Composite**  With thousands of composite combinations available, departments can choose what works best for their specific needs. That includes considerations like budget, the types (and frequency) of calls a department gets, or what’s worked well in the past.   But not every composite is possible. Every composite combination must not only meet NFPA standards to ensure it delivers the right level of protection but also be certified by a third party like UL. That means if a department loves a certain moisture barrier, it may not be possible to pair it with a different outer shell if it doesn’t meet NFPA minimums.   [![Get Everything You Need to Know About PPE With a FREE E-book!](https://no-cache.hubspot.com/cta/default/4744594/35f00484-99a4-4d66-987d-41de0d54b71f.png)](https://cta-redirect.hubspot.com/cta/redirect/4744594/35f00484-99a4-4d66-987d-41de0d54b71f) When selecting gear, departments should think about their local environment. A department in Florida will have different needs than one in Alaska. Some may prioritize heat protection, while others focus on mobility or breathability.  Also, keep in mind that material weight adds up. Composite weight is measured in ounces per square yard (oz/yd²). As a rule of thumb, every extra oz/yd² adds about a pound to the total weight of the gear.  In the end, choosing the right composite is all about finding the right balance between weight, breathability, thermal protection, and mobility. That’s why it’s so important to understand the numbers behind different composites—to compare composites, you must be able to understand the different advantages that each brings.  ### **Why TPP, THL, and Ret Matter**  When evaluating turnout gear, three performance metrics are especially important: **TPP**, **THL**, and **Ret**. Each one tells a different part of the story.  #### **TPP (Thermal Protective Performance)** TPP measures how long it takes for heat to transfer through the gear and cause a second-degree burn—especially during flashover events. The minimum TPP rating is 35.   To get a sense of what that means, divide the TPP by two. So, a TPP of 35 gives about 17.5 seconds of protection from direct flame exposure. The higher the TPP, the more thermal protection it provides.  #### **THL (Total Heat Loss)** For a long time, departments focused almost entirely on TPP. But high TPP often comes at a cost: heavier, less breathable gear. That can trap body heat and increase the risk of heat stress.  That’s why THL is now part of the equation. THL measures how much heat and vapor can escape from the gear. The higher the number, the more breathable the gear. The minimum is 205, and even a 20-point increase can make a noticeable difference for firefighters.  #### **Ret (Resistance to Evaporative Heat Transfer)** THL has been a part of the NFPA standard for a long time, but it doesn’t tell the whole breathability story. Some materials release heat well but don’t allow sweat vapor to escape efficiently. That’s where Ret comes in. Ret measures how well the gear supports evaporative cooling—essential for keeping the body from overheating.  A lower Ret means better breathability. Even a one-point difference can be felt. The maximum allowed Ret is 45, but most gear falls between 20 and 40. The most breathable composites can even achieve an Ret as low as 15.  ### **What Kind of Protection Matters Most?**  The best turnout gear strikes a balance between TPP, THL, and Ret. While TPP is measured in seconds of thermal protection, better breathability (higher THL and lower Ret) can give firefighters extra minutes of safe working time before heat stress sets in.  It’s also worth noting that gear design plays a big role. Even with the same composite, different manufacturers can produce gear with very different performance outcomes. For example, Fire-Dex’s [AeroFlex turnouts](https://www.firedex.com/aeroflex/) use AeroVent Technology to help sweat vapor escape more easily—boosting breathability beyond what the composite alone can offer.  But the first step for departments buying new turnout gear is to understand the materials they want and how the performance of those materials as a composite meets their needs. Gear manufacturers can help you think through those goals and find fits that maximize the performance of your chosen composite.   [![Explore Our Full Range of Turnouts!](https://no-cache.hubspot.com/cta/default/4744594/820570cd-a8ef-44f4-8d24-c699af90d2bf.png)](https://cta-redirect.hubspot.com/cta/redirect/4744594/820570cd-a8ef-44f4-8d24-c699af90d2bf)   Categorized: [PPE Performance & Safety](https://blog.firedex.com/blog/tag/ppe-performance-safety) [Previous](https://blog.firedex.com/blog/purpose-built-fire-investigation-ppe-designed-for-the-job) [Next](https://blog.firedex.com/blog/fire-dex-continues-a-tradition-of-award-winning-excellence) [![Share on Facebook](https://static.hubspot.com/final/img/common/icons/social/facebook-24x24.png)](http://www.facebook.com/share.php?u=https%3A%2F%2Fblog.firedex.com%2Fblog%2Fthe-turnout-gear-terms-you-need-to-know%3Futm_medium%3Dsocial%26utm_source%3Dfacebook) [![Share on LinkedIn](https://static.hubspot.com/final/img/common/icons/social/linkedin-24x24.png)](http://www.linkedin.com/shareArticle?mini=true&url=https%3A%2F%2Fblog.firedex.com%2Fblog%2Fthe-turnout-gear-terms-you-need-to-know%3Futm_medium%3Dsocial%26utm_source%3Dlinkedin) [![Share on Email](https://static.hubspot.com/final/img/common/icons/social/email-24x24.png)](mailto:?subject=Check%20out%20https%3A%2F%2Fblog.firedex.com%2Fblog%2Fthe-turnout-gear-terms-you-need-to-know%3Futm_medium%3Dsocial%26utm_source%3Demail%20&body=Check%20out%20https%3A%2F%2Fblog.firedex.com%2Fblog%2Fthe-turnout-gear-terms-you-need-to-know%3Futm_medium%3Dsocial%26utm_source%3Demail) ### Leave a Reply ### Recent Posts ### CATEGORIES - 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