For example, what if you receive fabric in a swap, decide to make a quilt from old clothes, or have thrift store items you want to repurpose? You may think something is cotton when it’s actually something else, or even cotton mixed with another fiber.
It’s important to know what you’re working with, as various types of fabric will react a bit differently once sewn into a quilt, washed and dried. For example, polyester won’t shrink while cotton will. You may not want to mix the two in a quilt. Plus, each type of fiber may require different laundering methods.
Image from Sew 4 Home.
If you’re purchasing fabric from a store you can verify the fiber content by looking at the information on the end of the bolt. It will tell you exactly what fibers the fabric was made from.
However, cuts of fabric, scraps, thrift store finds, clothing and more may not be accurately labeled. If you’re unable to identify the fiber content by touch, as many long-time sewists often can, it’s a good idea to do a burn test. In fact, a burn test is your best bet if you have any doubts at all about a fabric.
Burning a small amount of fabric will tell you a lot about the fibers used. How a piece of fabric burns, smells and the type of ash produced can give you a good idea of the fiber content.
Christine Haynes has written a good synopsis of doing a burn test. You’ll find it here.
For more in-depth information read this article by Janet Wickell for The Spruce Crafts.
Be sure to follow the safety precautions found in Janet’s article.
The following video from Sewing Parts Online demonstrates how various fibers burn.
A comprehensive burn chart, shown below, will be helpful in distinguishing between a variety of natural and man-made fibers. Click the link in the description below the chart for a larger version.
While you may not always be able to identify a fabric’s fiber content with 100% certainty, especially blends, this information should allow you to distinguish between cotton fabric and those containing other fibers.
Image Source: The image at the top of the page is from Textile School.