It’s T-shirt month! Of course, T-shirts are generally made of knit fabrics, and sewing knits can be a little intimidating.
But they’re really not that hard, as long as you know a few basic tips and tricks. Because knit fabrics have stretch, they require a few more considerations than woven fabrics for successful sewing. Here’s what you need to know to sew knits like a pro.
Use a sewing machine needle suitable for knit fabrics, such as a stretch or ballpoint needle. Ballpoint needles have a slightly rounded tip that’s designed to slip between the tiny knit loops rather than pierce them, causing tears and snags. Choose a needle size that’s appropriate for the knit fabric weight and thickness. Use sharp pins, such as silk pins, to avoid snagging the fabric.
Use all-purpose or polyester thread. These thread types are strong enough to withstand the fabric stretching without popping. If you are using a conventional sewing machine rather than a serger, consider using elastic thread, which allow the seam to stretch.
When cutting knit fabrics, use pattern weights rather than pins to secure the patterns and prevent shifting. To prevent stretching and distortion during cutting, make sure the cutting surface supports all of the fabric.
Use a compatible stitch on the machine or serger according to the knit fabric type and the garment area, and test-stitch or serge knit fabric scraps to determine theappropriate stitch and tension settings.
Sergers work very well for constructing knit garments, because the stitch is formed from multiple looped threads and includes stretch. Sergers vary from conventional sewing machines because they have two sets of feed dogs positioned one in front of the other under the throat plate. This allows for a feature called “differential feed,” meaning that the two feed dog sets can be adjusted to feed the fabric through the machine at different speeds. Differential feed is very useful for serging smooth knit seams because the varying speeds help guide the fabric without stretching it or creating a wavy edge. When using a conventional machine to stitch knit fabrics, use a stretch or narrow zigzag stitch.
When sewing knit fabrics, don’t stretch the fabric as you stitch, as that could cause wavy or distorted seams. Press knit seams using steam to help the fabric recover its shape and eliminate waviness after stitching.
Knit fabrics don’t ravel, so the seam allowance for most knit garment patterns is narrower than for woven garment patterns. It’s also not necessary to double-fold knit hems or finish raw edges. However, the tiny loops in knit fabrics snag and run more easily than woven fabrics, so use sharp scissors, rotary cutter blades, pins and needles to avoid catching and snagging the yarns.
If a knit garment requires interfacing, choose a knit variety that’s compatible with the fabric weight and hand.
Knit fabrics have varying degrees of stretch depending on the fiber content and specific knit structure. Patterns designed for knit fabrics include information about how much stretch is needed for the garment to fit correctly. If a pattern indicates that a fabric with 50% crosswise stretch is required, the fabric must double in horizontal length when pulled in the crosswise direction.
Some knit fabrics also stretch in both the lengthwise and crosswise directions, so check if the pattern calls for a fabric with “one-way” or “two-way” stretch.