The video above features untreated continuous multifilament polyester thread on the left, which burns vigorously once ignition temperature is reached, melts, emits black smoke and drips. Untreated aramid yarn on the right burns with difficulty because of high LOI. The flame extinguishes when the heat source is removed. Aramid does not melt but decomposes showing signs of thermal degradation.
Not to be confused with flame retardant, flame resistant yarns and threads are inherently non-flammable due to the materials they contain. When they are exposed to a flame they won’t ignite because the yarn or thread is unable to burn.
The flame resistance of these materials is built into their chemical structure, making them naturally resistant to an open flame from the inside out. Generally, flame-resistant yarns will not melt, drip, or support combustion from the air.
This includes familiar brand names like Kaneka Modacrylic Protex®-C, Performance Products Celazole® PBI, DuPont™ Nomex®, DuPont™ Kevlar®, and Kuraray Vectran™. Each of these can also be blended with other yarns and threads, including natural materials, to reduce the overall cost and still work well at extinguishing flames.
Non-Flammable Yarn Fiber Types
As you choose a yarn for your specific application, you’ll need to know the various levels of flame resistance and related properties. Here is a comparison of several inherently non-flammable yarn fiber types:
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Kaneka Modacrylic Protex®-C |
Protex®-C will not melt or drip when ignited. |
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Performance Products Celazole® PBI |
Celazole® PBI does not readily ignite or exhibit a melting point. |
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DuPont™ Nomex® |
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DuPont™ Kevlar® |
The melting point of Kevlar® is above 500 °C. |
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Kuraray Vectran™ |
Vectran™ has a melting point of 330°C and will generally degrade under UV light in a way that could reduce its melting point to closer to 220°C progressive strength loss starting at 220°C, melting point is not reduced through exposure to UV light. |
Common Uses for Flame Resistant Yarns and Threads
Flame-resistant yarns and threads are widely used in civilian general protective clothing, including gear for first responders and race car drivers. It is also used in bedding for flame-resistant mattresses.
Military combat and protective clothing such as coats, shirts, pants, gloves, and flight safety equipment must be flame-resistant under military specifications and the Berry Amendment. The mil-specs regarding these yarns and threads include A-A-50195, A-A-55195, A-A-55217, and A-A-55220. Service Thread’s A-A-59987 covers the requirements for a spun staple, meta-aramid sheath/polyester filament core and flame-resistant dye-able sewing thread. For more information about flame-resistant materials, contact the experts at Service Thread.
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