Primer: Sewing Knits
 
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Many new sewers are afraid of knits -- they shouldn't be -- you don't need to be an expert to turn out beautiful knit garments.

One of the great things about sewing knits is the leeway they give you when fitting. A garment made from a stretchy fabric doesn't have to fit as perfectly as one made from a woven, so knits eliminate the pressure of exact measuring and altering of patterns. And they're so comfortable to wear!

When constructing knit garments, one important rule to remember is that if the fabric stretches, the seams must stretch so the stitching doesn't pop as you bend and move in the garment. Whatever type of machine you have,  you can achieve flat, stretchy seams.

Whether made of cotton/polyester, cotton, wool, or synthetics,  each knit falls into one of several construction categories: single knits; double knits.

  • Single-knits like jersey, velour, terry, and fleece look different on the reverse side, have cut edges that curl, and usually have about 25-percent stretch.
  • Double knits like interlock tend to be more stable than single knits, often look the same on both sides, have cut edges that don't curl, and stretch from 25 to 75 percent, depending on the fiber and construction.
  • Rib knits, constructed from alternating knit and purl stitches in various combinations, may look the same or different on opposite sides, tend not to curl, and have up to 100-percent stretch.

It's important to always pre-treat a fabric before you sew it.  The general rule is to wash the fabric using the method you plan to use on the finished garment.   This means that cotton, linen, and synthetic knits should be washed and dried (in the dryer if you plan to dry them this way later), and wool knits should be steamed before cutting.

Smart pattern choices
When planning a knit garment, select a pattern specifically designed for knits, rather than for woven fabrics, because the pattern will have the correct amount of ease built into it. The amount of stretch in the fabric will determine the style and size pattern you choose. Check the pattern envelope for suggested fabrics and the amount of stretch required for the style. If you choose a fabric with less stretch, you'll need to add more ease.

Since knit fabric has built-in ease, you don't need as much ease in the pattern as you would for a woven fabric. For example, a couple of inches of bust ease  is plenty for a fairly fitted knit style, compared with the 5 in. of bust ease needed for most woven garments. And a double-knit skirt hangs nicely with 2 in. of ease, while a woven skirt would require at 3 inches or more.

Construction options
You can achieve excellent  results on knits whether you own a basic sewing machine or a high end serger. A good starting point is to use a long straight stitch of  9 stitches/in., stretching the seam as you sew it (as much as the fabric stretches easily) to add elasticity. When the seam returns to its normal length, the stitches are closer together and the upper and lower thread tensions have loosened. Zigzag or stretch stitches to construct seams aren't necessary, and in the writers opinion not as good..

For double knits that will stay pressed open, use a 5/8-in.-wide seam allowance. For single knits that tend to curl, use a 1/4-in.-wide seam, which you can finish two ways: either press it to one side and topstitch for a professional look, or sew a second line of stitching 1/8 in. from the first and then press to one side. The double-sewn seam adds strength and helps keep the seam flat.

If you have a serger, you'll find serging a quick way to assemble knits with a finished, factory look, and the seams will have built-in elasticity, so you don't need to stretch them as you sew. Make sure your stitch is balanced, adjusting the thread tension so that the stitch doesn't bind or ruffle the seam. If your serger has differential feed, raise the setting if your test seam looks wavy. For hemming soft knits, serge the edge, turning up a 1/4-in. hem, then topstitching twice to get a stable, non-slippery finish.

RAVELING REFLECTS CONSTRUCTION
 
Knits ravel or run only from horizontal cut edge, so edges generally require no finishing.
 
 
Wovens ravel from any cut edge, so edges require finishing.

Edge finishes

Most knits don't ravel, unlike some woven fabrics -- especially loosely woven ones, which can ravel until the seam allowance has vanished. So serging or otherwise finishing seam allowances isn't necessary with knits. Nonetheless, test whether your fabric ravels on a swatch--some silky knits ravel on horizontal cuts, but most cottons and wool knits don't.

You can sew an attractive hem on many knits with double-needle topstitching, the finish that's used most often in ready-to-wear.  Use a  4-mm-wide double needle and 9 sts/in. for a stretchy, professional-looking hem. If you're sewing a soft knit without much body, topstitching the hem, especially with a twin needle, may result in tunneling and rippled edges, since knits stretch more on the crossgrain.  You can stabilize the hem with strips of fusible interfacing, which also anchor the hem during stitching. Many sewers prefer two rows of topstitching rather than twin-needle stitching.

It's easiest to stabilize the hems before assembling the garment. Prepare the hems by pressing them into place. Cut 1/2-in.-wide strips of soft, all-bias knit fusible interfacing . Sew or serge the right side of a strip to the wrong side of the hem edge (adhesive side is up). After constructing the garment, fold the hem up, fuse it in place, and topstitch from the right side.


Ann Person of Eugene, OR, is the founder of the Stretch & Sew company of patterns and books.