Modern sewing enthusiasts have a wealth of options in terms of thread colors, weights and fibers. The two primary choices for thread fibers are polyester and cotton. While many projects and sewing instructions offer no recommendations for fiber type, there are a few differences between cotton and polyester thread. Many reported differences, however, are nothing more than myths and misconceptions.
Shrinkage and Other Aging Factors
Cotton is a natural fiber and subject to shrinkage. Hot water and heated drying cause cotton fibers to draw up tighter, resulting in changes to the size and shape of cotton fabric and threads. Alternatively, polyester is a synthetic fiber that is not subject to the same degree of shrinkage. This can present problems with how a particular project maintains its shape after several washes. Many sewing enthusiasts therefore recommend matching thread fiber type to fabric fiber type. For example, use cotton thread to sew cotton fabric and polyester thread to sew synthetic or synthetic blend fabrics.
Loss of Color and Bleeding
Natural and synthetic fibers absorb and hold color dyes differently. Certain types of cotton thread, for example, are more absorbent than polyester. During the dying process, cotton thread can absorb more dye, but not necessarily have the ability to hold onto the dye when washed. This can result in the dye bleeding onto nearby fabric. Polyester thread does not absorb as much dye and therefore does not retain excess dye that can bleed. To mitigate such problems, some cotton thread manufacturers wash the thread several times before processing it onto spools.
Hand Sewing Considerations
Hand sewing garments, quilts and other crafts presents different challenges than machine sewing. In many cases, sewing hobbyists who prefer hand sewing have a preference for one thread over another, based on the way it glides through fabric layers. Polyester thread, for example, often pulls through fabric layers with less snags and risk of knots. Cotton thread, when viewed closely, often appears fuzzier than polyester thread. Fuzz and loose fibers can create snags or small knots, leaving unsightly gaps in the fabric when pulled through.
Common Thread Myths
Myths regarding cotton vs. polyester thread abound. Common myths are frequently passed from one generation of quilters or seamstresses to another. Many quilters believe polyester thread will eventually cut through cotton fabric as a quilt ages and thus recommend against synthetic threads in quilts. Likewise, many sewing hobbyists believe polyester thread is stronger. Both myths are untrue. If a strong, heavy thread is used on a weak, thin fabric, eventually the fabric will tear under the strain. Whether the thread is cotton or polyester does not matter. Similarly, the tightness of spun fiber determines thread strength more than fiber type.
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