While the construction elements of a knit garment appear to be much simpler than those of a woven one, sewing with knits can be a bit more difficult, especially for beginners.
The amount of stretch, stitching style, and seam durability have to be carefully considered in the process.
Some very stretch knits, like jersey for example, can be quite flimsy and difficult to control in the alignment and stitching process. This is complicated by the fact that the cut edges tend to roll inward. The stretcher and thinner the knit fabric is, the more difficult it is to sew.
Knit fabrics have varying degrees of stretch, depending on the type of knitting application and the fabric's content. Knit stretchiness can be divided into three simple groups: semi stretch, medium stretch, and you guessed it, high stretch. The stitch style and sewing technique you use will depend on which one of these categories your fabric falls into. You can classify knit fabric into one of these stretch categories by testing a 3-inch square cut of your fabric.
- If the square stretches by only ½”, the knit fabric has little stretch (semi-stretch);
- If it stretches by 1”, the knit is considered to be of medium stretch; and
- If it expands by 2”, it is a high stretch knit.
Choosing The Right Machine Needle For Sewing Knits
Most knit seams should be stitched with a ball point machine needle.
A ball point needle has a curved (as opposed to sharp) needle point which allows it to slide in between the fabric threads as opposed to cutting straight through them. A ball point needle is gentler on knit fabric, minimizing the risk of damage and snagging.
Stitching Styles Used For Sewing Knit Seams
Stitch style is an important factor to consider when sewing with knit fabrics.
While it is perfectly suitable to use a straight stitch for most knits, you may want to consider a zigzag or any other similar style available on your home sewing machine. Your manual should indicate which stitches are best suitable for stretchy fabrics.
The structure of a zigzag stitch will provide more flexibility, especially along seams that require increased movement. Seams located at the armhole for example, are most susceptible to stress. For that reason, extra flexibility needs to be incorporated into these seams.
The beauty of zigzag stitching is that it does not require the use of stretchy thread. In addition, the fabric does not need to be stretched under the presser foot as you stitch. The zigzag structure alone provides enough stretchiness and give.
While a zigzag-like stitch is great for sewing very stretchy knit fabrics, it may not always be suitable for extra lightweight knits, or altogether necessary for knits with moderate stretch. A straight stitch should work just as well if the right type of thread is used, and the seam is slightly stretched during the stitching process.
To sew knit seams, a strong but stretch thread should be used when/if possible. A good thread should withstand movement without breaking the stitch. To add extra durability and control in the stitching process, use a shorter stitch length.
If using a straight stitch (not zigzag), the right choice in thread and stitch length should be used in tandem with manually stretching the seam as it is being stitched.
Stretching the knit layers in the machine stitching process adds “looseness” to each individual stitch such that when the knit seams are stretched during wear, they expand without breaking or causing strain on the rest of the garment.
To stretch a knit seam as you sew, hold the seam fabric layers with one hand in front of the presser foot and the other hand in the back of the presser foot. Gently stretch the seam as you stitch it.
As you stretch, the seam allowance will appear narrower. Don’t let this deter you- continue stretching and stitching at the same width throughout.
If the fabric was stretched too much during machine stitching process, the seam will appear to have mounds in it and not lay completely smooth. The individual stitches may also appear too loose.
On the other hand, if the fabric was not stretched enough in the process, the seam will gather up, and tension will be felt in the seam as it is being stretched.
Finishing Knit Seam Allowance Edges
The beauty of knit fabrics is that most do not fray or unravel when cut.
As with everything, exceptions do exist. Sweater knits, for example, unravel and can often have sensitive cut edges. For that reason, extra care should be taken when working with them.
For those knit fabrics that do not fray when cut, the seams can be left unfinished given that they do not roll maintaining their structure throughout. If the seam allowance edges lack stability, an overedge finish like a zigzag or serging stitch should be used to encase the cut fabric edges.
Some knits may appear to have crisp, stable edges when initially cut. After some use however, the seam allowance tends to lose its structure and start rolling inward. For that reason, it is always a good idea to finish all knit seam allowance edges with an overedge stitch regardless of how the fabric edges behave at the time of cutting and constructing the garment.
What Is Knit Recovery?
Recovery is term used to describe the “springiness” of knit fabrics. In other words, how fast do they bounce back to their original shape after being stretched, and how well do they adjust to the human form.
Conventionally, a high-recovery knit is considered a higher quality, better performing material.
The issue with poor recovery knits is that they often do not go back to their original shape/structure after being heavily stretched. It may take a wash cycle or other special treatment to force a garment with poor recovery to bounce back to its original shape.
When sewing a garment made of a low recovery knit, some seams may need to be specially reinforced in order to maintain their original structure and stability during wash and wear.