Aside from a burn test, which takes some set-up, time and effort, it is nearly impossible to tell from the feel and look of a fabric whether it is a cotton/poly blend or poly. I recently found a quick and easy way to distinguish between the two.
Fiber-Etch, a liquid used in embroidery or cutwork embroidery, dissolves any plant fiber including cotton, linen, and rayon. Since this product removes plant fibers, it is also useful to determine fabric content. With blends of plant fiber fabrics, the blended fibers will remain. For example, a cotton/polyester fabric will, when this product is applied to a small area, remove the cotton fiber and leave the polyester fiber.
So cut a small sample, paint on the Fiber-Etch and watch to see what happens. If it all disappears–it’s all cotton (or rayon or linen). If some of it disappears, it’s a blend and if none disappears, it’s poly.
Here’s a video demo on how to use Fiber Etch.
[youtube=http://www.youtube.com/watch?v=8ySucm_Aqs8&hl=en&fs=1&rel=0]
