Rayon is a manufactured fiber made from regenerated cellulose, a natural polymer sourced from wood pulp. Standard, untreated rayon is not flame resistant and is highly flammable. It behaves much like other common cellulosic materials, such as cotton or paper, igniting easily and burning rapidly when exposed to a flame.
The Inherent Flammability of Rayon
The core reason rayon burns so readily is its primary component: cellulose. Although chemically processed, rayon’s molecular structure is nearly pure cellulose, a long chain of glucose units. This structure is rich in carbon and hydrogen, which serve as excellent fuel for fire.
When rayon is exposed to heat, the cellulose undergoes thermal decomposition, a process called pyrolysis. This reaction releases flammable gases, like various hydrocarbons, which mix with oxygen in the air and ignite, sustaining a flame. Because rayon is a lightweight textile, it has a high surface-area-to-mass ratio, allowing it to ignite quickly and burn continuously.
Once ignited, untreated rayon burns with a bright yellow flame and produces little smoke, often smelling like burning paper or wood. It does not melt or shrink away from the flame; rather, it burns completely, leaving behind a light, soft gray or black ash that is easily crumbled. This rapid, complete combustion is characteristic of cellulosic fibers and presents a danger of rapid flame spread.
Standard Rayon vs. Other Common Textiles
Rayon’s combustion characteristics place it squarely in the category of highly flammable cellulosic fibers, similar to cotton and linen. These fibers all ignite at relatively low temperatures, around 255°C, and continue to burn after the ignition source is removed. They feed the fire by providing fuel and fall away as soft ash, unlike synthetic materials.
By contrast, synthetic textiles like polyester and nylon are thermoplastic, meaning they react to heat by melting. These fibers shrink away from the flame and form hard, hot beads of molten plastic, which can cause severe, deep burns if they adhere to the skin. While they do not spread fire as rapidly as rayon, the melting and dripping behavior introduces a different type of burn hazard.
Protein-based fibers such as wool and silk offer a higher degree of natural flame resistance. Wool requires a temperature of 570–600°C to ignite and needs an oxygen concentration higher than what is found in normal air to sustain burning. These fibers tend to self-extinguish or smolder when the flame is removed, making them inherently safer in fire situations.
Flame Retardant Treatments and Modified Rayon
Because rayon is inherently flammable, the fiber must be treated to meet fire safety standards for safety-critical applications. The textile industry achieves this in two primary ways: applying chemical finishes or creating modified, inherently flame-retardant (FR) fibers.
Chemical treatments, known as FR finishes, are applied to standard rayon fabric to change its combustion pathway. These finishes often utilize phosphorus-based compounds that work in the condensed phase, meaning they alter the solid material as it is heated. Instead of releasing flammable gases, the treated rayon dehydrates and forms a stable, protective layer of char on the fiber surface.
This char layer effectively insulates the underlying material and prevents the release of combustible gases, causing the fabric to self-extinguish when the flame source is removed. For applications requiring durability, such as children’s sleepwear or protective workwear, the flame retardant can be permanently incorporated into the fiber structure during the manufacturing process.
This creates FR rayon fibers where the chemical protection, often silicon or phosphorus-based, cannot be washed out. These modified fibers ensure the flame-retardant properties are integral to the textile, providing a consistent level of protection required for protective clothing and commercial furnishings.