Usually you’ll always know what the fiber content of your fabric is because the mill will list the contents on the swatch header or webpage. Sometimes, like in the case of deadstock or upcycled fabrics, you don’t have that content information. You can get fabric swatches tested for exact fiber content, but that can take time and the cost may not be worth it depending on your business. If you just need to know whether a fabric is natural fibers or not, there are a few quick ways to find out.
You can tell a lot about a fabric by the feel. Natural fibers, depending on the fiber, have a unique feel. They feel soft, but not slick. They generally, except for silk, aren’t shiny. Natural fibers also don’t tend to pill as much as synthetics in my opinion, so if you are looking at second-hand fabrics, this can be something to look for.
The temperature of the fabric against your fingers is another clue. Natural fibers tend to have a neutral temperature that doesn’t feel warm or cold to the touch. In contrast, a synthetic fabric like nylon feels cool to the touch.
A sure way to tell if a fabric is natural fibers or not is to burn a swatch of it. Of course, you don’t have the option to burn swatches in a store before purchasing, but you can check at home on a small swatch with appropriate safety precautions. Cut a small swatch – about 2” by 2” is plenty – and set a corner of it on fire with a lighter over a sink with water running. Let the swatch start to burn for a few seconds and then run it under the water to extinguish the flame before it gets close to your fingers. If the swatch burned with a visible flame and the burnt edge crumbled smoothly into a lightweight ash, then the fabric contains natural fibers. If the swatch didn’t have much flame and left a rough, scratchy, or curled edge, then it is majority synthetics. Natural fibers burn. Synthetics will melt and then harden like plastic because that is what they are.