In the latest installment of our Know Your Fibers series, we’re taking a look at two of the dominant fibers used in multiple industry applications: cotton and polyester. Most people know that cotton is a natural fiber and polyester is a man-made, synthetic fiber. These differences are just the beginning, however, so let’s take a deeper dive on the unique properties of these fibers and how they’re processed.
Harvested from plants grown annually, cotton fibers are composed of pure cellulose. Cotton fibers have a hollow opening in the middle, called the lumen, that runs the length of the fiber. When the boll opens and the fiber dries in the sun, the lumen collapses. This dynamic causes the fiber to twist and form convolutions. Cotton fibers are naturally coated with waxes to protect them from the elements, therefore, cotton is a naturally hydrophobic (water repellent) fiber.
Interestingly, cotton is known in the marketplace for its absorbency; however, the fiber will remain hydrophobic unless subjected to a purification process to remove its inherent waxes and oils. After removal of the oils and waxes, the fibers become absorbent.
Cotton is comfortable and breathable. It’s soft and natural. It’s hypoallergenic. All of these properties make cotton the natural fiber of choice for nonwoven hygiene products, from feminine pads to baby care and adult incontinence.
But cotton has an even greater array of attributes suitable for a variety of nonwoven applications. In the fiber world, the strength of cotton is considered moderate to above average. The strength (tenacity) of cotton is 3.0-5.0 grams/denier when dry. This fiber is unique in that its strength increases when wet to 3.3-6.0 grams/denier. Cotton has a natural moisture regain of 8.5% under normal temperature and humidity conditions. It also features a heterogeneous length distribution.
Finally, cotton maintains its relevance and popularity in a modern era defined by environmental concerns, because it’s both sustainable and biodegradable.
Polyester (polyethylene terephthalate) is derived from a chemical reaction involving petroleum, air, and water. This artificial fiber is comprised of purified terephthalic acid (PTA) and monotheluene glycol (MEG).
Polyester is thermoplastic, meaning it can be melted and reformed. When making polyester, chemists melt polyester pellets and force them through small holes (spinnerets). On the exit side of the spinnerets, the continuous filaments of what we know as polyester fibers solidify. The size and shape of the hole dictate the shape and diameter of the fibers. The fibers are solid polymer; there are no void spaces inside the fibers. These continuous filaments—called “tow”—can be cut to any length (there is no length distribution, all fibers are manufactured to be perfectly homogeneous) to produce staple fibers for use in textiles and nonwovens, or they can be left as a continuous monofilament, which resembles fishing line.
Polyester is hydrophobic. For this reason, polyester fabrics don’t absorb perspiration, or other fluids, leaving the wearer with a moist, clammy feel. Polyester fibers typically have a low level of wicking. Relative to cotton, polyester is stronger, with a greater ability to stretch. Fiber strength can range from 2.5 grams/denier to 9.5 grams/denier.
Environmentally concerned purchasers frown on polyester use. Since it’s a man-made fiber derived from petroleum-based products, polyester is not considered sustainable, nor is it biodegradable.
Cotton and polyester couldn’t be more different. Cotton is natural, breathable, absorbent, and sustainable. Polyester, on the other hand, is a synthetic fiber that doesn’t breathe well, repels water, and isn’t sustainable.
But keep in mind that you’ll see cotton and polyester blended together to produce fabrics that exhibit properties that can’t be achieved using either fiber alone. Taken separately, each has its advantages and disadvantages. The more you know, the better choices you can make when selecting a fiber to meet your needs.
Silk is an amazing textile. It’s breathable, hypoallergenic, all-natural and beautifully soft. Given its many superior qualities, it’s not surprising that manufacturers have created a host of man-made products that try to mimic the look and feel of real silk. At the top of the list is polyester, a material made from petroleum biproducts that really has nothing in common with silk except texture.
So how do you tell the difference?
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Silk is made from the protein fiber produced by silkworms to weave their cocoons. The cocoons are dissolved in boiling water to extract the filaments which are then spun and woven into cloth. This process leaves small imperfections in the weave, variations that can be found in all types of natural fiber. Polyester, on the other hand, is a synthetic material made by heating petroleum biproducts and carboxyl acids to create a polymer compound. This is then stretched into fibers which are either spun or twisted together. The result is a perfectly uniform cloth with no tiny flaws in the weave. Look at the weave. If you can see tiny bumps or uneven threads, it’s more likely to be genuine silk.
Both silk and polyester have a distinct shine. With silk, the shine comes from the structure of the fibers which are like miniature light-reflecting prisms. The shine in polyester varies as a result of blending the polymer with other materials like cotton, satin or real silk. Even on its own, however, polyester is invariably shiny and becomes even more so with wear, age and ironing. Unlike silk, however, the shine in polyester is always “white”. Genuine silk changes color when you tilt it, refracting the light as it passes through the prisms in the fiber. Move the cloth in front of a light source. If the shimmering is just a consistent white shine, it’s polyester. If the reflected light changes color, it’s probably silk.
Most high-quality patterned silks create the design by weaving different colored threads into the fabric. It is possible to print patterns onto silk, however, so seeing a printed design doesn’t automatically mean you’re looking at polyester. There’s an easy way to tell the difference. Printed silk patterns can be seen from both sides of the material while polyester doesn’t allow the pattern to show through to the other side. Turn the material over. If the pattern doesn’t show through, it’s not silk. Most patterned polyester fabrics will simply be backed by a solid color.
If you gently rub a piece of silk, it will feel soft and yielding. Pushing your finger into the fabric, you should feel a slight “give” in the weave. When you rub genuine silk, your fingers will begin to feel slightly warm, something that doesn’t happen with polyester. Rubbing two pieces of silk together should make a crunching sound, a bit like walking on snow or crushing cornflakes. Run the material through your hands and pay attention to the sound it makes and any heat it gives off. If you’re playing with polyester, the result will probably be “nothing”.
It’s not foolproof but checking the price tag is often your first clue to what you’re holding in your hands. Sericulture, the process of raising silkworms for textile production, is an expensive business. Most of the world’s silk is produced in China and India, and there’s an increasing focus on even pricier organic production which is sustainable, humane and uses zero chemicals. All that adds up to a cost that can be ten times as high as polyester, an entirely man-made substance that’s much cheaper to mass produce. If the price is on par with cotton or man-made fibers, it’s unlikely to be real silk. About the only way to get a bargain is to go to the source, and even in Asia silk cloth doesn’t come cheap.
The ultimate test is to set fire to the cloth, something that’s neither practical nor recommended. Real silk smells like burning hair and produces ash while polyester basically melts and smells like plastic. You shouldn’t have to use a match, however, to know whether you’re getting the real thing. Just take the time to really examine the fabric and be prepared to open your wallet for an item that should maintain its beauty, texture and color for a lifetime.
Now that you’re an expert, you shouldn’t have any trouble recognizing the authenticity of Brave Era’s 100% silk travel sheets. Nothing compares with silk when it comes to hypoallergenic comfort, breathability and luxurious softness. Treat yourself to a great night’s sleep wherever your adventures take you and relax with the comfort of knowing you won’t be bringing home any unwanted companions like nasty bugs and germs.
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