With the array of thread available, how do you know which thread is best for your project? The following are some guidelines to help you select the perfect thread for your project.
General Thread Rules
Color: Pick thread that is one shade darker than the fabric.
Weight: Match the thread weight to the fabric weight. Threads are ranked by a number system. A high number indicates a light (or fine) thread, and the medium weight of thread is a 50 weight.
Fiber: Try to match thread fiber to fabric fiber. Cotton fabric should be sewn with cotton thread; polyester or manmade fiber should be sewn with polyester thread. If possible, don't sew natural fibers with polyester thread. Polyester fiber is stronger than most natural thread, so over time, the stronger polyester thread can break the weaker cotton fiber of the fabric. For quilting, look for thread labeled "machine quilting" or "hand quilting."
Twist: The amount of spin of the thread fibers. A thread with a high amount of twist will be smoother, shinier and stronger than thread with little or no twist.
Types of General Sewing Threads
For general sewing, use thread spun from cotton, polyester or a polyester/cotton blend. Specialty threads change as often as consumer tastes change.
Rayon thread: Designed for machine embroidery, it has shine to give the embroidered design a decorative effect. Rayon thread is perfect for rolled edges on your serger. Use it in the upper looper only.
Metallic thread: A man-made thread which is ideal for machine-embroidery or decorative serger finishes.
Basting thread: A lightly twisted thread used to hand- or machine-baste garments together. Easily broken, it's typically made of cotton fiber and available in white. Try using basting thread for fitting garments prior to sewing.
Invisible thread: Great for blind hemming or when it is difficult to match colors. It's typically made of a single strand of polyester and has no color. Because of the lack of color, it is difficult to see. Its one drawback is that it can be stiff and distort the fabric. I use invisible thread in my blind hemmer for hemming pants, draperies and other projects.
Buttonhole and carpet threads: Heavy duty and designed for heavy fabric where additional strength is desired. Often used for hand-sewing, it will work in the bobbin of most sewing machines and can give your sewing a decorative effect.
General purpose thread: A medium-weight thread made from cotton, silk, polyester or a blend of cotton and polyester.
Cotton is usually mercerized. This is a finishing process that makes the thread smooth and shiny and adds strength. Cotton mercerized thread is ideal for woven fabrics that require little or no stretch in the seams. Cotton is also heat-resistant, making it a better choice for quilting because of the need for pressed, consistent seams.
Silk is natural fiber that is strong and very fine. It has some stretch which makes it a better choice for topstitching or tailoring when the fabric needs some shaping and some give.
Polyester is suitable for most fabrics because it has some stretch. It is a better choice for knit fabrics but may break cotton fibers if the knits are designed with cotton fiber.
Blended threads are suitable for knits, wovens, man-made or natural fabrics. Blended threads are typically designed with a cotton filament wrapped around a polyester core thread giving the thread both durability and stretch. Plus, the cotton fiber makes the thread heat-resistant.
Serger threads are available in the same fibers as general sewing threads, with the exception of woolly nylon. Woolly nylon is a nylon thread that has little or no twist. Used in the upper looper for a rolled edge or in the upper and lower loopers for lingerie sewing, this thread is designed to gently relax after it's sewn and cover the edge finish. It has lots of stretch and is soft against your skin. Its one drawback is that it will melt in the dryer or under a hot steam iron.
Most serger thread is sold by the cone. Look for cone thread that is tightly wrapped and consistent in width. When using your serger for edge finishing, don't worry too much about matching the thread color. Most serger owners will invest in the basic colors of thread, black, brown, gray and white, to match the edge finishes as needed. If using your serger for seaming and edge finishing, it's the outside needle that creates the seam. Often, just matching this thread to the fabric is enough.