Is Spandex Flammable? Analyzing the Combustion Characteristics of Elastane

Spandex (also known as elastane or Lycra) is renowned for its unparalleled high elasticity and comfort, making it widely used in sportswear, medical textiles, and home furnishings. But is this high-performance fiber safe in a fire? Does it burn or self-extinguish? This article will deeply analyze the chemical properties of Spandex, its flammability rating (LOI), the three main flame retardant technical routes, and testing standards to help you fully understand the application value and safety advantages of Flame Retardant (FR) Spandex.

Key Takeaways:

• Spandex (Elastane) is a highly flammable synthetic fiber with a low Limiting Oxygen Index (LOI) of 18-20%.
• It burns rapidly, melts, and produces hazardous molten drips due to its polyurethane chemical structure.
• Flame Retardant (FR) Spandex is created using three main methods: co-polymerization (inherently FR), additive blending, or surface finishing.
• “Inherently FR” (co-polymerization) offers the most durable and stable fire resistance, lasting over 50 wash cycles.
• FR Spandex is essential for safety in protective wear (EN ISO 11612) and home furnishings (NFPA 701).

Does Spandex (Elastane) Actually Burn?

Yes, Spandex is a highly flammable, high-elasticity synthetic fiber.

Chemically, Spandex (Elastane) is a polyurethane fiber. Due to its molecular structure, which is rich in carbon-hydrogen bonds, it decomposes easily when heated and releases flammable gases. When exposed to an open flame, Spandex will rapidly curl, melt, burn, and be accompanied by black smoke and molten drips. These drips can ignite other materials and cause severe secondary burns to the skin. Furthermore, burning polyurethane decomposes to produce toxic gases, such as isocyanates, and has a pungent, acrid odor.

Why Does Spandex Burn Easily? A Chemical Structure Analysis

The fundamental reason for Spandex’s flammability lies in its polyurethane chemical structure, which is high in hydrocarbon content and has a low thermal decomposition temperature.

Spandex is primarily composed of soft-segment polyether or polyester-type polyurethane. This structure has two critical weaknesses regarding fire resistance:

1. High Hydrocarbon Content: The molecular chains contain a large number of –CH₂–, –O–, and –NH– groups, which are all combustible components.
2. Low Thermal Decomposition Temperature: Spandex has a relatively low ignition point, beginning to thermally decompose around 230°C–260°C. It rapidly cracks and produces flammable gases like carbon monoxide and hydrocarbons, leading to a very fast burn rate.

Combustion Characteristics of Spandex

The specific behavior of Spandex when burning differs significantly from other fibers:

Property	Spandex (Polyurethane) Combustion Behavior
Ignition Difficulty	Easy to ignite
Burning Speed	Fast
Flame Color	Bright yellow flame
Burning Residue	Molten black beads
Odor	Pungent, acrid (toxic fumes)

Spandex’s Flammability Rating: What is its Limiting Oxygen Index (LOI)?

The Limiting Oxygen Index (LOI) of Spandex is approximately 18%–20%, classifying it as a highly flammable material.

The LOI (Limiting Oxygen Index) is the core metric for measuring a material’s flammability. It represents the minimum concentration of oxygen required to sustain combustion. Since the oxygen concentration in the air is about 21%, any material with an LOI below 21% will continue to burn in the air after being ignited.

Spandex’s LOI is well below this 21% safety threshold, meaning it can self-sustain combustion in the air and is not self-extinguishing.

LOI Comparison: Spandex vs. Other Fibers

Compared to common textile fibers, Spandex’s flammability is at a high level, You can click on the different fibers listed in the table below to view detailed information regarding their combustion or flame retardant properties:

Fiber Type	LOI (Limiting Oxygen Index)	Flammability Class
Spandex (Polyurethane)	18–20%	Flammable
Cotton	18%	Flammable
Polyester	20–22%	Combustible
Nylon	20–22%	Combustible
Acrylic	18.5%	Highly Flammable
FR Polyester	≥28%	Flame Retardant
Modacrylic	28–32%	Flame Retardant
Aramid	28–30%	Flame Retardant / Self-extinguishing
Fiberglass	>100%	Non-combustible

How is Spandex Made Flame Retardant? The Three Major Technical Routes

Because Spandex is inherently flammable, it must undergo chemical modification or finishing techniques to achieve flame retardant properties. These technologies primarily rely on three mechanisms: gas-phase dilution, char-layer insulation, and free-radical trapping. Commercially available FR Spandex is mainly produced via the following three routes:

Route 1: Co-polymerization Modification (Inherently FR)

This is the most advanced and stable method. During the Spandex polymerization stage, flame-retardant monomers (like DOPO derivatives or phosphate polyols) containing phosphorus, nitrogen, or silicon are introduced, making the FR elements a permanent part of the molecular chain. This is the core technology behind Begoodtex FR Spandex , ensuring permanent, wash-durable safety. Learn more about our Inherently FR Spandex fabric.

• Advantages: The FR property is permanent, stable, non-migratory, and durable to washing (over 50 cycles).
• Disadvantages: High cost, complex synthesis process, and potentially a slight reduction in elasticity.
• Effect: The LOI can be increased to 28–30%, achieving a “flame retardant” classification.

Route 2: Additive Flame Retardant (Physical Blending)

This involves physically adding flame retardant powders or liquids (such as phosphorus, nitrogen, or composite FR agents) into the Spandex spinning solution or polymer system.

• Advantages: Relatively simple process and lower cost.
• Disadvantages: The FR agents can easily migrate (leach out) and have poor wash durability (performance may degrade after 10 washes).
• Effect: The LOI is increased to 24–27%.

Route 3: Surface Flame Retardant Finishing (Post-finishing)

This applies a flame-retardant coating or impregnation finish to the surface of the finished Spandex fiber or Spandex-containing fabric (like a poly-spandex blend). Common systems include phosphorus-nitrogen (P-N) finishes (e.g., Pyrovatex, Proban) or silicone coatings.

• Advantages: Suitable for blended fabrics, with minimal impact on elasticity and hand-feel.
• Disadvantages: The poorest wash durability, with performance typically degrading after 20-30 washes.

How is Spandex FR Performance Tested? Common Methods and Standards

Flammability tests primarily focus on the burning rate, self-extinguishing time, melting/dripping behavior, and mass loss rate to determine if the fabric meets specific safety standards. Different applications correspond to different test standards:

• NFPA 701 (USA): Primarily used for curtains, drapes, and other hanging textiles. Requires the sample to self-extinguish within 2 seconds of the flame being removed, with less than 40% mass loss, and no flaming drips.
• EN ISO 11612 (EU): The standard for protective clothing. Tests include the heat transfer index (HTI) after 10 seconds of contact with a 650°C flame, among others.
• FMVSS 302 (Automotive): The US standard for automotive interior materials. Requires a horizontal burn rate not exceeding 100 mm/min.
• BS 5852 (UK): Used to assess the fire performance of upholstered furniture (like sofas).

Typical Application Scenarios for Spandex

The core value of Spandex lies in its high elasticity (stretching 5 to 8 times its original length) and excellent recovery. It is rarely used alone. Instead, it is blended as a functional component (typically 2%–25%) with fibers like cotton, polyester, and nylon, finding wide use in apparel, home textiles, and industrial applications.

Apparel Applications (2%–25% Spandex)

• Sportswear/Activewear: Provides high stretch, sweat resistance, and breathability for yoga pants, cycling gear, compression wear, and swimwear (5%–20% Spandex).
• Denim/Stretch Trousers: Offers comfort-stretch and wrinkle recovery (2%–5% Spandex).
• Intimates/Shapewear: Requires a soft, close fit for body shaping (10%–25% Spandex).
• Socks/Hosiery: Maintains shape and prevents sagging (2%–10% Spandex).

Home Textiles and Industrial Applications (2%–10% Spandex)

• Home Furnishings: Used in stretch-fit sofa covers, mattress ticking, and seating fabrics to improve fit and prevent wrinkling. When used in public spaces (like hotels, theaters), they must be flame-retardant treated to meet NFPA 701 or BS 5852 standards.
• Industrial Protection: Blended with FR cotton or aramid (e.g., 97% FR Cotton + 3% FR Spandex) to add comfort and mobility to protective garments (meeting EN ISO 11612).
• Medical Textiles: Used for elastic compression bandages and braces to provide stable pressure control.
• Transportation Interiors: Used in aircraft, subway, and automotive seating fabrics, which must be FR-treated to meet standards like FMVSS 302.

Conclusion: Spandex is Flammable, but Can Be Used Safely with FR Technology

Spandex is indeed a flammable fiber (LOI 18%–20%), but through durable flame-retardant technologies (especially co-polymerization or high-performance finishing), it can achieve fire safety while retaining its elasticity.

In an era where textile safety is increasingly important, companies can choose different FR solutions based on the application. For industrial protective wear, an inherently FR Spandex blended with FR cotton/aramid is the choice. For home furnishings, a durable FR coating that passes NFPA 701 is required. Flame Retardant Spandex is becoming the ideal choice for combining comfort with safety.

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