Serging Stretchy Fabrics

By Naomi Baker

• The stretch factor is found in both woven and knit fabrics, provided by spandex blended with fibers such as nylon, cotton, rayon and polyester. Although spandex originally was used for leggings, swimwear and undergarments, garments ranging from sportswear to eveningwear now boast the advantages of this added stretch element.
  
  
• Spandex adds stretchability, provides shape retention, minimizes wrinkling and adds resiliency to a fabric.
  
  
• The spandex amount in a fabric determines its stretch. Small amounts--from 1% to 5%--are added to woven and knit fabrics for loose-fitting garments, while the addition of 10% or more gives the needed stretch for body-hugging action--and swimwear.
  
  
• Many spandex-enhanced fabrics will stretch in both directions for maximum comfort.

• Many patterns are available for stretch fabrics, all requiring the stretch factor for proper fit. Because fabrics vary in stretchability, compare your chosen fabric's give to the pattern requirements. If the percentage of stretch is different, you'll need to compensate on the pattern to achieve the fit, going down in size for fabrics with more stretch or adding to the garment width for fabrics with less stretch.
  
  
• To determine the stretch, fold the fabric on the crosswise or lengthwise grain, several inches from the cut edge or selvage. Measure 4" of the fold, then stretch. If it stretches to 5", it has 25% stretch; if it stretches to 6", it has 50% stretch; etc. (Figure 1).

Figure 1

Stretch 4" on the fold to determine stretch amount.

• Always begin with a new sharp 9/65 or 11/80 needle; a dull needle may cause holes along the stitching line. A stretch or ball point needle will penetrate the fabric easily and prevent snagging, cutting the spandex strands or skipping stitches. For topstitching or finishing hems, use a 2.5/75 or 4.0/75 stretch twin needle.
  
  
• Serger, all-purpose or texturized stretch nylon threads all are appropriate for stitching stretch fabrics. For very stretchy fabrics, use texturized stretch thread in the needle to tighten the needleline and add additional stretch in the seam. Use texturized stretch thread in the loopers for soft comfort. Loosen the tensions slightly so the thread is fuzzy and stretchable; if tensions are too tight, the thread may cut the fabric.

• The three-thread balanced and two-thread wrapped seam options provide the most give for even the stretchiest fabrics. Tighten the two-thread needle tension so the lower looper thread wraps the edge snugly. For the most stretchy seam, use both needles in this stitch (Figure 2).

• Adjust for a medium-width and -length stitch. To prevent wavy seams, adjust the differential feed to a plus setting and lengthen the stitch (Figure 3). For seam and hem finishing, serge with a medium to narrow balanced two- or three-thread seam.
  
  
• Test-serge parallel to the stretchiest grain, then stretch the seam as in wearing. If the seam breaks (usually the needle thread), loosen the needle thread slightly or change to texturized stretch nylon thread in the needle. If the thread continues to break, stretch the fabric slightly while serging.
  
  
• Stabilize shoulder seams with 3/4"-wide self-fabric strips (cut on the least stretchy grain), 5/8"-wide Seams Great™ or 3/8"-wide clear elastic. Cut the reinforcement strip the same length as the pattern shoulder seam. Place on the seamline and serge through the strip (Figure 4).

To prevent stretched seams, adjust to plus differential feed and lengthen stitch.

Figure 4

Serge over reinforcement strip to stabilize shoulder seam.