How thermal simulation could be a game-changer for the fire-resistant clothing industry

Fabric might be the last thing on your mind when firefighters rescue someone from a burning building, but without fire-resistant clothing, such rescues might not happen at all.

The turnout gear that firefighters wear is highly engineered and informed by the latest trends in materials science. Standard gear includes multiple layers, such as an outer shell, moisture barrier, and thermal liner. Wearability, which comes down to weight and flexibility, has to be balanced with cost, performance, and durability.

Proximity suits are another type of high-temperature apparel. They are used in even more extreme conditions than municipal fire-fighting, such as metalworking, furnace operations, industrial and specialized firefighting, and emergency response. A surprising array of materials are used to make these articles to achieve optimal thermal performance. For example, a common proximity suit design features super-thin aluminum layered with plastic to create a shiny surface. The suit isn’t designed to reflect visible light, but rather invisible electromagnetic wavelengths like infrared light, which convey heat.

Slow-burning innovation

Innovation can be an especially slow process for the heat-resistant textile industry. Product development is expensive: every design iteration has to be exposed to intense temperatures to test its “thermal performance.” This comes in addition to concerns that all manufacturers have: How much will it cost to make? How much can a design be optimized without hindering overall performance?

The timeline for innovation gets even longer for heat-resistant textile manufacturers because of the strict standards their products need to satisfy. Every time a company adjusts how they design or manufacture a textile, the new version may need to be recertified, even if the changes are slight.

Because of these challenges, many heat-resistant fabric manufacturers work with research and development (R&D) laboratories to support the innovation process, like the Bal Dixit Laboratory for Advanced Materials and Fire Protection Research at Rochester Institute of Technology (RIT).

Known more commonly as the Bal Dixit Lab, companies work with researchers in the lab to validate product designs, as well as to perform preparatory tests ahead of submitting products to standards bodies like ASTM International and UL. The lab was opened in 2018 through a $2 million gift from an RIT alumnus and founder of Newtex Industries Inc., Sudhakar “Bal” Dixit.

The lab’s test capabilities include standard vertical flame, radiant protective performance (RPP), and thermal protective performance (TPP) tests. These are based on specific standards set by ASTM International (ASTM D6413, F1939, and F2700, respectively).

The lab can also conduct less common test methods, including smoke optical density, based on ASTM E662, and a “sub-scale” thermal resistance test that is comparable to ASTM E119. These capabilities give companies access to standards-level testing but at a smaller scale; less material for samples is needed, which can significantly cut costs while offering results that are representative of performance during full-scale tests. Other standards-relevant tests include heat resistance of fabrics and panels, smoke density for wire insulation, and thermal-protection performance (TPP) of textiles. Ultimately, these capabilities give companies information that they can use to fine-tune designs ahead of official standards and certification testing.  

Labs like the Bal Dixit Lab are especially useful for clothing manufacturers that use thermal-protection fabrics to make suits, gloves, and other protective apparel. Those manufacturers tend to be smaller and further down the supply chain from the primary manufacturers of the heat-resistant fabrics that they assemble into clothing. As such, they generally lack the internal R&D resources that larger original fabricators of textiles may have.

Thermal simulation for everyone?

Peter Martin is a materials scientist at RIT’s Golisano Institute for Sustainability who manages research at the Bal Dixit Lab. He believes the fire-resistant textile industry’s innovation cycle—clothing manufacturers in particular—could be accelerated through the use of simulation technologies.

Thermal simulation uses digital modeling to determine how the textile materials making up a heat-resistant article of apparel will behave when exposed to varying levels of heat. Consider the firefighter turnout gear mentioned earlier. This gear needs to protect the firefighter from thermal exposure, be light and flexible enough not to impede movement, and be cost effective and durable. For Martin, optimizing the composition, thickness, and sometimes even the order of the layers in thermal apparel presents an opportunity for manufacturers to not only make more efficient products that meet existing standards, but to discover the key material properties that drive product performance.

“Standards tests have limited value when it comes to R&D,” Martin explained. “For example, they will tell us that a glove will protect someone’s hand when exposed to 500 °C for 15 seconds, but that only describes how that glove performs under those very specific conditions.”  

According to Martin, this is a fundamental problem, especially for manufacturers without extensive R&D capabilities.

“The results of standards testing leave companies no wiser as to why the glove performed well or not,” he noted. “Without this basic understanding of material properties, they often can’t predict how their products will work in the more generalized real-world conditions where their customers are using them.”  

A thermal simulation of the glove would mathematically represent the properties of its layers when exposed to an external heat source, a much faster and less expensive process than subjecting a physical sample to actual heat in an experiment. The model would expedite product development, giving designers a reliable picture of how different material combinations might perform in diverse contexts.

Simulated exposures can also be used to resolve questions about how a garment might perform in a specific situation. For instance, a model can be used to find the top temperature that a glove will protect a worker long enough to perform a task, like fixing a bolt inside a large furnace chamber. This type of calculation can be important for processing companies that use large furnaces with very long cool-down times. Real-world scenarios like this are not addressed through standardized testing, but are important to making decisions about how and when heat-resistant textiles can be used.  

Of course, models are not the same as the real world. But they can give a design team more confidence in drilling down to ideas with the best potential. And that means less time and money spent on abandoned prototypes.   

Multi-layer garments

Martin believes that thermal simulation could be of especial value to companies that make multi-layer, fire-resistant clothing, which are complex articles to design and produce. Garment manufacturers combine fabrics they source from original manufacturers, each utilizing materials as varied as spun glass (fiberglass), plastic, aluminum, ceramics, and silica to achieve thermal protection.

A single multi-layer, heat-resistant article can rely on as many as four or five different base materials in its composition. Clothing makers need to calculate the tradeoffs between the strengths and weaknesses of each in their prototype designs, an already complicated process that grows exponentially when it comes to multi-layer articles. Thermal simulation, Martin argues, would dramatically speed this innovation cycle, allowing designers to simulate the performance of different combinations of fabrics.

But thermal simulation can’t happen until the key material properties that dictate performance are known.

Unlocking material efficiency

Research needs to be done to define and quantify the material properties of common fire-resistant fabrics on the market that influence overall product performance. This heavy lift at the front end of thermal simulation is beyond the budget of most manufacturers of multi-layer garments—this is where resources like the Bal Dixit Lab have a critical role to play.  

Martin, during his time at the Bal Dixit Lab, set into motion research that could bring thermal simulation to all levels of the thermal-protection textile industry. In partnership with a national standards body, he led the early phases of a project to develop a framework tool that would be widely available to manufacturers.

The lab’s efforts reflect GIS’s larger efforts to enable sustainable industrial practices. Producing fire-resistant textiles like aluminized, acrylic-coated, or fiberglass-woven fabrics—to name only a few varieties—is very energy- and resource-intensive. By enabling better design practices, a thermal simulation framework would not only benefit a business’s budget, but also efforts to counter climate change.

Thermal simulation makes it easier to design textiles that are as lightweight, materially efficient as possible. From a sustainability perspective, the math is simple: using less materials and energy equals fewer emissions going into the air and raw materials extracted from the earth.