Silk, a fabric synonymous with luxury, can be pricey and difficult to maintain. While silk does have some limitations, the results of a sewing project made with silk are often worth the cost. On the other hand, polyester mimics some of the more desirable characteristics of silk, making polyester a viable and less expensive alternative for garments originally intended only for silk. While the fabrics have differences, silk and polyester are sewn using many of the same techniques.
Prewash your fabric the same way you would wash the finished item. Silk is washable and does not, like most natural fibers, shrink. However, the weave of a silk fabric tightens when washed, giving a shrinking effect of up to 5 inches per yard of fabric. So, it's important to wash silk before cutting out the pattern pieces. Polyester, because it is a synthetic fiber, does not shrink when washed or dried.
Pin the fabric and pattern pieces using small shaft pins, such as silk pins. These pins are less likely to leave a permanent hole in fine fabrics such as silk and polyester. Cut out the pattern pieces using sharp scissors, as dull scissors are particularly prone to chew on silky fabrics.
Sew using a thread made of the same fiber as your fabric, either polyester or silk. Using the same fiber-based thread blends the stitches into the fabric. It also is more likely to wear in the same manner as the fabric itself, creating a more consistent look over time. Avoid using cotton thread, which is too heavy and causes the stitches to look more pronounced.
Use a short sewing machine stitch, which is better for sheer or thin fabrics as this size stitch blends into the fibers. This type of stitch also provides a measure of support for seams, as thinner fabrics don't possess as much body and strong seams as heavier fabrics.
Finish the raw seam edges using an appropriate seam finish, such as a clean-finished seam. To sew this seam, fold the edge of the seam allowance under to the inside of the fabric by an eighth of an inch and stitch near the fold. A serger machine can also provide a finished seam edge for both silk and polyester fabrics.
Iron the finished garment, craft or decor item on low to medium heat and use a pressing cloth. Polyester is not a high-heat tolerant fabric and may melt if exposed to too much heat. Silk scorches and turns yellow if exposed to high heat.
Silk fabrics can be put into the dryer, but should only if the fabric has not yet been cut in preparation for sewing, as the weave may tighten and shrink the length of the fabric piece. Finished garments that were not put in the dryer before being sewn should never be dried in this manner.
Polyester, because of its tendency to melt when exposed to high heat, should not be used for children’s sleepwear.