Polyester and elastane fabric
We’re just about ready to get started with cutting and sewing the bodysuit, so let’s take a look at some of the basic techniques and stitches you’ll need when sewing with stretch fabrics. No, you don’t need a serger! But if you happen to have access to one, this is a great opportunity to fire it up because it’s an amazing tool for spandex sewing.
There are a couple of main challenges you might encounter when sewing with stretch fabrics. If the stitches don’t have enough give, the threads will break when the seam is stretched. If the stitching is too dense or the fabric is overstretched during stitching, the seams will have ripples. With the correct machine settings, though, these problems can be avoided.
It’s a good idea to spend some time experimenting with stitch types and techniques, so you’ll have everything ready when you move on to your actual project. This is especially important if you’re using metallics or faux leather for your final version, since these materials tend to show permanent stitching marks and you’ll want to get it right the first time.
For most spandex fabrics you’ll be happiest with a stretch needle. Note that stretch needles and ballpoint/jersey needles are not the same thing – both have a slightly rounded point so that they slide between the fibers of knit fabrics instead of puncturing them, but stretch needles have a deeper scarf (indentation above the eye on the back of the needle) as a precaution against skipped stitches. This makes them a better choice for sewing elastic and fabrics with high spandex content. A universal needle will also work in many cases if that’s all you have, and a sharp or microtex needle may be a useful alternative on coated fabrics like pleather and vinyl. If you’re getting skipped stitches, switch to a different type or go down a size.
A good-quality 100% polyester all-purpose thread is ideal for knits. (Not cotton – it doesn’t have enough give). If you’re on team serger you can also try using texturized (woolly) nylon thread, which has a fluffy texture and outstanding stretch. Use it just in the loopers, or in both loopers and needles for a really stretch-proof seam (you may need to grab a needle threader). It can also be used in the bobbin of a conventional sewing machine, though you’ll need to wind it by hand. Be careful with the iron around woolly nylon seams, because heat is nylon’s great weakness.
Some people recommend a walking or even-feed foot for sewing stretch fabrics, but in most cases special feet aren’t necessary. The one exception is for pleather and vinyl, for which you’ll most likely want a walking, Teflon, or roller foot to prevent sticking.
The easiest way to give your seams some built-in give is with a zigzag stitch (which nearly all home machines can do) or a stretch stitch (which may or may not be available on your machine). Check your manual for stretch stitch options, and try them out to see if you like them. My machine’s main stretch stitch is a triple straight stitch, which I don’t recommend for this purpose. It’s slow, it’s very difficult to remove in case of mistakes, and it chews through thread at an amazing rate. If your machine offers the “lightning bolt” stitch this can be a good option – it’s like a zigzag but the stitches are angled backward and forward, so it’s narrower and produces a cleaner-looking seam. (Different manufacturers use different names for this stitch, but the symbol is usually similar).
Believe it or not, you can sometimes get away with a regular straight stitch if you shorten your stitch length (I set mine a little below “2” on the stitch length dial) and stretch the fabric a little bit as you sew. Stretching as you sew takes a little practice, but it can make a big difference in the longevity of your seams. To do it, place your hands in front of and behind the foot and pull evenly from both sides. Make sure you’re letting the feed dogs move the fabric and not yanking it through, as you can break the needle or even screw up your machine’s timing if you’re not careful.
Try out a couple different stitch options before committing to your actual bodysuit, because the correct settings will depend on your fabric to some degree. Check what the seams look like from the outside, and make sure they don’t pull open or dimple the fabric too much. A straighter stitch will make it easier to press the seams open, if you want to, but pressing them flat is usually fine for knits. For extra security, do double-stitched seams: sew a narrow zigzag on the stitching line and a wider zigzag just outside it, then trim close to the second line of stitching.
If the seam is a little wavy after sewing, try steaming it back into shape with the iron. If it’s very wavy, you might need to try adjusting the machine settings. Reducing the foot pressure can help if your machine has that option, or try a walking foot. Lengthen the stitch length if possible, but not so much that you compromise the stretch of the seam. If wavy seams continue to be a problem, you may need to stabilize them. For shoulder seams and other areas that don’t need to stretch much when worn, fuse a narrow strip of knit interfacing along the seam line to firm it up. For seams that need to stretch, try a temporary wash-away or tear-away stabilizer.
On a serger, you’ll do most of your seaming with a 3- or 4-thread overlock. The 3-thread is nice because it gives you the option of a narrow or wide stitch, depending on whether the right or left needle is inserted in the machine, but for a very close fitting bodysuit you’ll probably want the extra security of the 4-thread seam. Stitch a sample or two in your actual fabric before you begin, and take a look at the resulting seam to make sure your settings are appropriate. The needle threads should be tight enough that the seam doesn’t pull open from the right side, but loose enough that they don’t snap when the seam is stretched along its length.
The differential feed is your serger’s secret weapon, so make good friends with this dial. It’s especially helpful when sewing squirrelly stretch knits, because you can increase the differential feed to get rid of wavy, stretched out seams or decrease it if your seams are puckering.