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Weekend Wonders with Fabric.com: How To Make Flat Felled Seams

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As part of our Weekend Wonders series with Fabric.com, we have a couple technique tutorials designed to make those Wonders go more smoothly, look more professional, and... simply give you an upper hand when it comes to impressing friends with your vast sewing knowledge. Making a flat felled (or flat fell) seam is a detail with a place in history as well as a place in the world of professional seam finishes. You can find references to the flat felled seam technique in vintage as well as hand sewing (once the only way to sew anything!).  And, if you look down right now at the inside seam of your jeans, you'll see a trademark flat felled seam.

Within the flat felled seam family there’s the French seam, mock French seam, Hong Kong finish, overcast, overlock, and coverstitch. Each of these make the wrong side of the seam look as good as the right side. Some can only be made with a specialty machine, but the standard flat felled seam can be completed with your regular sewing machine. It takes a bit more time than a standard seam, and, as we mention so often in our tutorials, requires accuracy. 

Okay... back to your favorite pair of jeans. The flat felled seam is usually on the inside seam as well as the crotch seam (where there’s the most stress). Flat felled seams are known for being strong, durable and comfortable for the wearer. They’re also ideal for anything that will be washed repeatedly. Although this seam works well in denim, it’s not usually recommended for fabrics any heavier; the seam would be way too bulky. (We have a solution for this... keep reading through to the last section of the tutorial).

If you’re not a jeans-wearin' kind-of-person, you may have noticed flat felled seams on men's clothing, such as dress shirts and even boxer shorts. It's also a go-to choice in children's clothing. We're willing to bet it’s the durability aspect of the flat felled seam that makes it popular on garments for men and kids! 

Other types of projects perfect for a flat felled seam finish include: various types of bags, active wear, skirts or dresses, garments made of sheer fabrics, or reversible garments. In reality, you can use a flat felled seam anywhere that calls for a straight or vertical seam. 

From a design standpoint, creating a flat felled seam is a great way to finish a garment (or other type of project) while adding distinctive detail and texture. This is how we used it in our Weekend Wonder's Reversible Summer Apron coming up at the end of the week.

Plus, depending on the fabric type, you can use a variety to threads and thread colors in the final steps of sewing a flat felled seam for a unique, customized look. 

Some of the projects we’ve done at Sew4Home with flat felled seams, include: the EZ-Grocery Bag, French Market Tote, our little girl's Shirred Sundress, and the Italiano Kitchen Mama Apron and Bambina Apron

The tools and machines you need to sew a flat felled seam  

You need the appropriate needle for your fabric type. For example, in the case of a flat felled seam on jeans, you should use a denim needle

The appropriate thread for construction is important too, and how you want your final seam to look will dictate the thread you use. In our jeans example, you need a stronger thread in a heavier weight. Look for Dual Duty XP Plus Jeans from Coats, which comes in that exact red-orange topstitching color that can be so hard to match. And since we're sewing jeans in our head right now, you might also want to look for Coats' Denim thread. It's an all-purpose weight, but comes in a perfect blended denim blue color.

Besides a regular or topstitch thread, you could also use a rayon for shine, or metallic for a touch of bling.

The sewing machine foot you use is also an important element. In our example below, we use a standard presser foot. Our Sew4Home studio machines are supplied by Janome, and their standard presser foot has a little black button on the back that is used to lock the foot in place when going over an uneven (or bulky) seam. It works like a charm for this technique. 

Some manufacturers have a foot specifically designed to sew flat felled seams, called a felling (or lap seam) foot. This type of foot is designed with a groove for the raised fabric in the seam. You can also use the foot to roll the fabric over and sew it in place all at one time. Check with your local sewing machine retailer for information about this type of foot and to find out if it is available for your make and model of machine.

Other important tools include sharp scissors for trimming the seam, such as appliqué scissors or a shorter blade scissor. You may find marking your seam allowances is helpful; if so, you'll need a fabric marking pen or pencil and a clear ruler. We find a seam gauge to be handy for folding the raw edge of the flat felled seam to ensure our seam is consistent from the first line of stitching. And, since a flat felled seam can be finished with two lines of parallel stitching, you can use a twin needle to sew two evenly spaced rows of stitching at once.

In regards to machines, as we mentioned above, your standard sewing machine is just fine. However, you can use a specialty machine for flat felled seams. Janome has a felling guide for their 1200D professional serger. With this machine and attachment, you can create a flat felled seam with a cover stitch underneath. You can also create a similar seam with the Janome Coverstitch machine.  

In commercial production, there are actual felling machines that only sew flat felled seams. That’s how they make all those pairs of jeans so fast!

A few other notes about seam allowance and direction

Seam allowance is an critical part of this process. The type of project you’re sewing dictates the seam allowance used. In garment construction, a ⅝" seam allowance is standard, whereas in home décor projects, bags, etc., a ½" seam allowance is most common. You need to be very careful about seam allowance, because in flat felled seams, one side of the seam is trimmed away to ⅛" or ¼". If you’re following a pattern or tutorial, the seam allowance and the amount to trim will be indicated. If you’re incorporating flat felled seams into your own project, be sure to test first on scraps so you can determine your trim amount. 

You also need to think about the direction of any flat felled seam before you sew it. In a garment, you always want the side seams to fold toward the back. This means you have to sew and trim each side of a garment differently. 

Speaking of directions, a flat felled seam can be done on the inside or outside. It all depends on how you start the technique: right sides together or wrong sides together. We illustrate both below.

Once you’ve sewn flat felled seams,you will eventually have to cross them with another piece (waistband, lining, etc.), which means you need to be prepared to sew over the “hump” of the seam. For this, you can use the little black button trick we mentioned above (provided you have a Janome), or use what’s called a hump jumper. 

Advanced seamstresses can sew a zipper into a flat felled seam or insert a sleeve (or armscye) with a flat felled seam. You can find information on how to do these techniques in sewing books and on the Internet. We're sticking to straight seams for now.

Sewing an outside flat felled seam 

In our examples below, we’ve used a light colored polka dot fabric so you can see the right side versus the wrong side. We also used various thread colors for the same reason. No style points... just clarity!

  1. Place your fabric edges WRONG sides together. Pin in place as needed.
  2. Setup your sewing machine for a standard straight stitch.
  3. Sew a straight seam, with the appropriate seam allowance. We used ⅝" in our example.
  4. Open out the fabric and press both sides of the seam allowance in one direction. (See our note on seam direction above.)
  5. Trim the lower (the underneath side) seam allowance. We trimmed ours to ¼".
  6. Here’s where the super accuracy comes into play! Fold the fabric so it is again wrong sides together. Lay it on your work surface so the fabric with the uncut seam allowance is on the bottom. Fold in the uncut seam allowance edge to meet the cut seam allowance edge. Press in place. 
  7. Pressing well is super important. To help with accuracy, you can use a seam gauge to check that the folded-in edge to the cut is the same distance as that from the line of stitching to the cut. 
  8. Open the fabric flat, then press the seam flat in the same direction you originally pressed. 

    NOTE: Depending on your fabric type, you can use a temporary adhesive to hold the layers in place.
  9. Edgestitch along the folded edge (We used purple thread for this step).  Remember, since we’re doing an outside flat felled seam, we are working on the right side of the fabric.
    NOTE: Since you’re sewing through a few layers here, you may want to adjust your stitch length depending on the fabric type.
  10. Congratulations! You’ve sewn a flat felled seam.
  11. In case you’re wondering (you were wondering, weren't you?), here’s what the wrong side looks like.

Sewing an inside flat felled seam

  1. Place your fabric edges RIGHT sides together. Pin in place as needed.
  2. Following the same steps as for an outside flat felled seam, press the seams to one side, trim away the lower seam allowance, fold the raw edge under on the upper seam allowance, press in place. 
  3. Edgestitch along the fold.
  4. Anything look a little different? Beside the flat seam being on the wrong side of the fabric, you only have one line of stitching on the right side.
  5. You can leave it this way, or you can add another line of stitching.
  6. Simply sew another line of edgestitching on the right side of the fabric. (We used teal thread for this step.)
  7. Below is a picture of the outside flat felled seam (bottom) and inside flat felled seam (top). Can you see a difference? Not really, right? 
  8. The difference is where the bulk of the fabric sits. On inside flat felled seam, it's on the inside. On the outside flat felled seam, it's on the outside. So how do you know which one to use? It’s partly personal choice, and partly determined by the type of fabric.

Mock flat felled seam option

For a quicker version of the flat felled seam, there is what’s called a mock flat felled seam. This also works well on heavier fabrics that otherwise would be too bulky for the traditional flat fell seam (remember.. we promised you a solution for heavier weight fabrics). In the end, you have a similar looking finish from the outside. 

  1. Place fabric right sides together.
  2. Set up your sewing machine for a standard straight stitch.
  3. Sew a straight seam, with the appropriate seam allowance.
  4. Here’s the difference: finish the edges with a zig zag or overcast stitch on your sewing machine, or overlock using a serger. We opted to use a serger.
  5. Press the seam allowances to one side, as in the above steps (remembering direction as you did above as well). 
  6. Using a straight stitch, sew two parallel lines on the right side of your project. There aren't any hard-and-fast rules for determining exactly where to sew the two lines. A good rule of thumb is to first sew along the “well of the seam," just as you would when edgestitching. Then, move the needle to a left position, and use the foot itself as a guide to sew an even distance from the first line of stitching. This would also be an ideal time to use a twin needle! 
  7. Here’s what the mock flat felled seam looks like from the front and back.
  8. We used a variation of this technique in this toddlers apron tutorial made with laminated fabric. Since laminated fabric can be a bit bulky, this seam finish worked out perfectly, plus it made our apron look quite professional.

A final word about specialty threads

If you’ve decided you want your flat felled seam to have a little pizazz, you can use a specialty thread, such as those mentioned above. It is recommended you use a standard, all-piurpose thread to construct the seam (to make the first seam). Then, re-thread your machine with your chosen specialty thread and sew the edgestitching as well as an optional additional line of stitching. This works especially well for the inside flat felled seam and mock flat felled seam techniques.


Sample Creation and Instructional Outline: Jodi Kelly



Comments (19)

Lori Miller said:
Lori Miller's picture

I love the tutorial. I seen this technique used for applying binding to a quilt. I can't seem to find it again. I am currently trying this process but it's not working. Would you know how to use it for putting binding on a quilt? Do you maybe know of a tutorial that would show how?

Liz Johnson.Editor.Sew4Home said:
Liz Johnson.Editor.Sew4Home's picture

@ Loti Miller - Sorry, that's a new one on us. I don't have any resources to pass along. It seems like a quilt would have a lot of layers to try to trim back in order to create this type of finish. 

anne p. said:
 anne p.'s picture

i, too, am over 60 and i learned how to do freench and flat fell seams in Home Ec.  Your tutorial is a very helpful refresher.  clear instructions, thanks!! 

melle@featheredruffles.com said:
melle@featheredruffles.com's picture

I've been cheating. Just doing french seams and stitching them down. I hate exposed seams, so on pillowcases and, well, everything, I do french seams to hide the stitches. That can get bulky ln flannel... especially once you're doing my makeshift *felling* of the french seam to that it lies flat... I think I'll give this a shot on a project I'm working on now... It's this or the HK, and I'm not sure I'm understanding the HK yet... it appears to be just... binding the edges... We'll see.

Thanks for a great, clear tutorial. (I have a brother and have one of those black buttons, had NO IDEA what it was for! hehe)

Faye Stirn said:
Faye Stirn's picture

I work for a uniform shop how do I do this step when the shirt needs to be taken in 2 inches on each side and have the finished double seam on the sides??

Liz Johnson.Editor.Sew4Home said:
Liz Johnson.Editor.Sew4Home's picture

@ Faye Stirn - We're sorry, but that is a pretty specific garment alternation question that isn't something we can trouble shoot long distance. You likely need to take out both side seams, including the bottom part of the sleeve, take up the additional inches needed, remake the flat felled seam, first then re-insert and re-stitch the bottom of the armhole. Sew4Home doesn't really focus on garment construction, so you would probably be better off with expertise from an alternation resource. 

Martha Adams said:
Martha Adams's picture

The best tutorial.  Explained with great pictures the difference in doing front or back .  Have a felling foot, but having a difficult time using it. Thanks

TX granma said:
TX granma's picture

I am over 60 and learned to make flat felled seams in 8th grade.  Too bad Home Ec isn't taught anymore.  I am glad there are blogs like this taking up the cause.

Tsgrandmama said:
Tsgrandmama's picture

I'm also over 60 but did not learn to make a flat felled seam in Home Ec.  I just discovered this  tutorial and it is great!


mizrae13 said:
mizrae13's picture

This tells me it's time to hone my sewing skills and take a step towards more professional finishing.  

Marilyn Adams said:
Marilyn Adams's picture

Your fabrics are so beautiful, I love the colors.   I especially like the turquoise and pinks which would be perfect in my bedroom.

grandmas place said:
grandmas place's picture

just love this tutorial, would this same technique apply to hemming or can you show us a tip on that


Liz Johnson.Editor.Sew4Home said:
Liz Johnson.Editor.Sew4Home's picture

@ grandmas place - Flat Fell seaming is not a hemming technique. However, a cover hem is, as well as overlocking the raw edge of the fabric to prevent raveling prior to final hemming - both done with a serger. Both make the inside of your hem, look as nice as the outside, like a flat fell seam. The only other thing we could think of is if you were going to put a separate contrasting fabric at the hem of something and wanted to use the flat felled seam technique as a way to join to the two fabrics, but then you would still have to use a standard hemming technique at the edge of the second fabric.

JosieB said:
JosieB's picture

I am always learning something new on this site.  Love the look of flat felled seams, but have never tried them.  Your  tutorial was just what I needed.  Also, that little black button on my Janome pressure foot has come in handy many times. 

EllenB said:
EllenB's picture

Another one of your super tutorials!  I do have to comment on the photo for step 6 - someone new to sewing may not understand that you can't press on the cutting mat - I'm assuming your iron is not heated!

Rosemary Bolton said:
Rosemary Bolton's picture

I have always wanted to learn this... I mean, I have made these sorts of seams, but I never knew what they were called.

That hump jumper looks very handy. It would probably save a lot of frustration working with thick fabrics

Thank you for this. I am going to print it out, as I have done with many of your other techniques for tricky things, and add it to my notebook.

This website is my favorite place to learn and be inspired.

Katie L said:
Katie L's picture

I'm always interested in ways to improve my skills and make my projects look more professional. I can't wait to play with this skill later today. Great tutorial! Very clear step by step directions! You make it look fairly easy (which i'm sure it is with a little patience and pratice  )

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