Polyester is a versatile and popular fabric, a staple of the textile industry. According to Global Market Insights, polyester had a $91.7 billion market valuation in 2020.
If you work in the welding, firefighting, or molten steel industries, the question racking your mind is probably this: is polyester flame resistant?
Polyester is not flame resistant; it is just difficult to burn and will continue burning until you extinguish the flame. Since it is harder to ignite than most natural fibers, industry insiders consider it non-flammable.
Keep reading as we explore why polyester is not flammable and what manufacturers do to make it acquire flame retardant capabilities.
What is Polyester?
Polyester is a synthetic fiber made from long chains of chemically bonded molecules (polymers). These bonded chains become longer and more flexible and develop into fibers that you can eventually make into polyester fabric.
Polyester manufacturers can cross-link the polymer chains with other molecules to make them more stable. The resultant polyester fiber will be durable and highly resistant when exposed to heat or moisture.
Since polyester is a durable and rugged material with hydrophobic properties, it is ideal for outerwear, luggage, tents and tarp.
Is 100% Polyester Fire Retardant?
The common misconception is that 100% polyester fabric is fire retardant. The main reason is people misunderstand the meaning of “non-flammable” and “flame retardant.” Polyester fabrics are not flame-resistant fabric.
On the Limiting Oxygen Index (LOI), polyester has an LOI of 20-22. Industry players consider materials above an LOI of 26 as having flame retardant properties. Although not quite at flame retardant levels, polyester is pretty close to that mark, which makes it difficult to burn. It is higher than cotton, which has an LOI of 17-19.
LOI refers to the flammability of fabric. It is a measuring method that determines the minimum concentration of oxygen needed to burn a fabric or textile. In short, the higher the LOI, the more resistant it is to combustion.
For instance, as you can see from the chart below, rayon has an LOI of 17-19, acrylic 18-20, while modacrylic has an LOI of 28-32.
Is Polyester More Flammable Than Cotton?
No. If anything, cotton is one of the most flammable fabrics on the market, which is hardly surprising. As a general rule, natural fibers, of which cotton is one, tend to be combustible. The only natural fiber that does not catch fire easily is wool.
Does polyester burn easily?
As seen above, cotton has an LOI of 17-19, while polyester stands at 20-22. It has low thermal conductivity, so it won’t transfer heat quickly. That means polyester will not burn as easily as cotton.
Additionally, polyester has a melting point of 356°F (250°C) and igniting point of 1022°F (550°C), while the cotton will ignite at 410°F (210°C). That’s because polyester molecules are held together by strong covalent bonds, making it harder for oxygen to get in and start a fire.
Which burns faster?
Cotton fibers are cellulose based, the same material as paper. As a result, they are long and wispy, providing a greater surface area for oxygen, a catalyst for fire. The thinner it is, the closer it is to resembling paper, and that explains why cotton burns rapidly when you expose it to fire.
On the other hand, polyester fibers contain chemicals that make them harder to burn than cotton. And it burns slowly, at about 1/3 as fast as paper. Additionally, it has a higher molecular weight, which makes them more difficult to ignite. Polyester burns vigorously only if you combine it with another fiber.
What Happens When Polyester Catches Fire?
When polyester catches on fire, it tends to burn slowly, unlike most natural fibers. Moreover, polyester will melt and drip when it ignites, so it can cause secondary injuries to your skin. For this reason, you should not wear polyester as underwear or baselayer.
If anything, you should avoid wearing synthetic fiber clothing (nylon, acrylic) under your FR clothing. When it catches fire, the melting debris will drop into the inner garment and start burning. Note that the melted polyester will cause deeper burns over a concentrated area.
We proceed a burn test both on the surface and edge of 100% polyester mesh fabric. It’s commonly used for creating quick-dry polo and T-shirt.
After burning, the upper part of the picture shows that the fabric is burned through and shrinks much. While the lower part of the picture shows that the burning edge melted.
Can Polyester Fabric Be Flame Resistant?
Yes, you can make polyester fabric flame resistant. There are two main ways to go about it:
Polyester lamination is the process of covering polyester with a fire-resistant (FR) backing fabric. The procedure involves heat sealing a layer of polyester between 2 layers of FR backing, creating a laminate material with FR properties.
Polyester is an excellent material for this because it is more durable and stable than the other forms of synthetic fiber base films (nylon and polypropylene). It is the most reliable and rigid option for laminate finishes, running anywhere from 1.2-10 mil thickness.
Polyester produces light, high-quality laminate with great FR qualities, which explains why manufacturers typically use it to make softshell jackets with FR and antistatic properties.
The concept is pretty similar to lamination, except that this time you coat a lightweight 100% polyester with FR polyurethane (PU) coating applied to both sides. That will improve its flame resistance.
Other advantages of coating polyester are that it becomes waterproof and increases its strength and durability, eliminating tearing, ripping, and fraying. Consequently, its use cases involve rain jackets and pants, transfer sleeves, and chutes.
The Bottom Line
Numerous articles mistake polyester for being flame resistant because it is difficult to burn, but it is not flame resistant. Sure, 100% polyester is not flame retardant, but it can obtain FR properties through processing it in several ways to make it compliant with PPE standards like EN 14116 and EN 11612.
While it’s not quite at flame retardant levels, which have LOIs over 26, polyester is not that far off at 20-22. It certainly is less flammable than cotton at an LOI of 17-19. Further, polyester will only burn once it gets to 356°F.
Polyester has strong molecular bonds and lower thermal conductivity, so it is harder to burn than natural fibers. Transforming it into a flame retardant (FR) fabric is as easy as laminating or coating it with FR material.
Never use polyester or any other synthetic fabric for your base layer or underwear. When polyester catches fire, it will melt and cause severe secondary burns concentrated on one spot.
On the other hand, if your flame-retardant outer garment burns through, the molten debris from the fabric will have the opportunity to ignite your synthetic fiber inner garment.