Open seams are probably the most used seam in many sewing projects. It may be one you have been sewing with on many different occasions without realizing it. Open seams are simple and straightforward, just the opposite of closed seams. The seam allowance, or edges after the seam has been sewn, are pressed open. In contrast, a closed seam has the edges encased in the seam itself.
Open seams are quick and easy to sew, but because the edges of the seam show and can fray, the seam needs to be carefully neatened. The neatening is necessary if the seam is going to be visible on the reverse side of the item.
Seams add the definition and shape to the garment and are the best way of connecting the pieces. Don’t confuse open seams with a plain seam. A plain seam is stitched and then the whole seam is pressed to one side, while the open seams are pressed open.
Seams that are enclosed in a lining would not need to have their edges finished. Seams sewn with a serger are neatened automatically as the serger does the job of sewing, cutting and neatening all in one simple seam. However, there are occasions when open seams are machined and needing some neatening. If you don’t have the luxury of a serger you may be looking at how to keep open seams tidy and stop the edges from fraying.
Read my article on sewing terms if there is anything you do not understand in the article.
How to Sew Open Seams
Firstly, here are the four steps to take to sew open seams. This is followed by four ways to neaten open seams once you have completed the seam successfully.
Step 1 - Optional Finish
At some point, you will need to finish the raw edges of your seam allowance. This can be done on the pieces before the seam is sewn or after. My preference is always to finish the seams at the end but on rare occasions, your pattern will specify to finish the raw edges first. See the finishing options after the seam instructions.
Step 2 - Stitch the Seam
Put the right sides of the fabric together. Match any notches or markings together to get an accurate seam matching. It is advisable to cut notches pointing out and not cut into the fabric edge.
Step 3 - Press Open
Press your seam open on the wrong side of the item. The edges may already be neatened if you did that at the beginning in step one. The iron should be used in an up and down motion rather than dragging it along which may distort the seam line. Read more about pressing fabric for sewing.
Step 4 - Finish the Seams
If you didn't finish the seams before, now it the time to do so. There are four choices set out below.
Seam Finishes for Open Seams
As previously mentioned, the order of finishing the seam edges is a personal choice. Some sewers like to do it before the seam is completed and some like to do it last. Either way is perfectly fine.
Here are four different ways to finish off and neaten the edges of open seams.
A serger is a separate machine specially designed for finishing seams. For open seams you need to make sure your seam allowance is at least ½ inch (12mm) as the width of the serged stitches is usually at least ¼ inch (6mm). In most cases, you will trim the minimum amount of fabric with the serger knife. Read more about how to use a serger.
Using pinking shears is a quick and easy way to neaten the raw edges of open seams. Simply hold the two raw edges together and cut along the edge with the pinking shears. The jagged or zigzag edge will prevent the edges from fraying. Pinking shears need to be kept sharp to cut fabric without burring so never use them to cut paper or anything other than fabric.
Using bias tape to enclose the edges of a seam creates a very neat edge and stops the edges from fraying. This method of finishing is often used to neaten unlined jackets, inside bags, and for quilted edges. It can be a contrast to the main fabric or made out of the fabric itself as a self-made binding. There are two methods you can use to add the bias tape - Hong Kong finish or a regular bias bound seam. My preference is the Hong Kong seam which is what I have used in the photo below as the stitching is almost invisible when done in a matching color thread. On a regular bias bound seam, you can see the stitching on the bias itself so you need to be a little more accurate.
A simple zigzag stitch along the edge of the fabric when it has been pressed open will neaten the edges and prevent fraying. You can use a simple zig-zag stitch or a 3 step zig-zag. Stitch a small way in from the raw edge to prevent the edges from rolling over and causing bulk. You can trim closer to the zig-zag if necessary.
What are Open Seams Used For?
Open seams are the most useful seams for sewing on plain cotton. The good thing to note about open seams is the bulk of the fabric from sewing two pieces together is spread on either side of the seam when the open seam is pressed open. The open seam is the best seam for the sides of skirts and dresses and the side seams of trousers too. Open seams are used on the sides of a blouse pattern under the arm and to sew up the side seam of the sleeves.
The pattern pieces you use will often have markings to guide the joining of the open seam. Notches to indicate a meeting point should be cut outwards for matching purposes. Once the notches have been matched the seam neatening will trim off the notches.
Tips for Pressing Open Seams
Remember to test your fabric first and make sure your iron setting is at the right temperature for the kind of fabric you are using. A presser cloth, to lay down on top of the fabric, enables you to press down directly onto the seam with some pressure. A further pressing with the tip of the iron along the join of the seam gives the seam a clean, neat open finish. Read more about the best pressing tools for sewing and pressing fabric for sewing.
Open Seams in Stretch Fabric
Although stretch fabrics are wonderful to sew because they need not be finished, getting the right stitch for open seams is sometimes a bit tricky. You will need to practice on a scrap to get it right before setting foot on your good stretch fabric.
Here are some tips to bear in mind as you sew open seams on stretch fabric.
- NEEDLE - Change your needle on your machine to a ballpoint needle or a stretch needle. Ballpoint pins are advisable too. This prevents snagging and allows for a smoother stitching line.
- DON'T PULL - Do not be tempted to stretch the fabric as you sew. Let the stretch fabric feed through the machine without pulling. If you pull the fabric your open seams will pucker.
- SUPPORT - Don’t let the fabric drag to the ground and pull on the garment as you sew. Support the fabric somehow so the seam is not pulled out of shape.
- STITCHES - Reserve some scraps to practice on and use a small zig-zag stitch instead of a straight stitch. The reason is a zig-zag stitch will stretch with the fabric and not snap when the fabric is pulled or worn.
- FINISHES - A stretch-knit seam does not need neatening. Ideally, a serger is the best machine to use for the stretch knit fabric. The serger seam would be finished all in one action.
- READ MORE about how to sew stretch fabric.
Open Seams - In Conclusion
Plain and simple is really the label that attaches itself to open seams. It is the most widely used seam and the one best used for simple cotton dresses and tops. Open seams are a good starting point for the new sewer, but also a ‘go-to seam’ for tried and tested garments made by the experienced sewer.