Flying High! – Mastering Fly Fronts

The words fly fronts and intimidating are often used in the same sentence. Yes, fly fronts look complicated. There are lots of ways to sew them, and everyone has their preferred way (or no way, if you’ve never done one).

I thought I’d share My Way with you, which I learned when I was a fashion student. I remember totally messing it up in the exam! But 30 years on, I’ve had more practice and made plenty of patterns for fly fronts.

Here’s a hand drawn overview, followed by step-by-step photos.

Step 1 Pieces

All the pattern pieces for making a fly front.
The fronts need a 1.5cm seam allowance and a zip notch to mark where the bottom of the zip will be. Make sure the zip notch isn’t in the curved part of the front.
The fly shield will go behind the zip so no-one sees your undies if your zip comes undone. The pattern piece can be curved like this one or simply rectangular. Cut 1.
The fly facing is typically curved like this one. Cut 1, but pay attention to which way you cut it – the facing here, cut right side up, will make a left-over-right opening as used traditionally for menswear. Flip the pattern piece over to cut a right-over-left opening.
Making your own pattern pieces for a fly shield and fly front.
If you’re making your own pattern pieces, the facing and shield need to be 2cm longer than the zip notch is from the top (for example, if the notch is 18cm from the top edge of the front, these pieces will need to be cut 20cm long).
Sometimes the facing is half the width of the shield as in this case, but it doesn’t have to be. Facings can be much wider, but don’t cut the facing any narrower than 5cm (or it will be too narrow for the zip and topstitching). I favour about 6cm.
As mentioned above, the shield can simply be a rectangle.
Checking the zip notch on a fly front pattern.
The bottom stop of the zip needs to be just above the zip notch – it can’t be below it. I’m using a plastic zip which is too long, but I’ll shorten it from the top. If your zip is metal, it’s best to use a zip which is the correct length.
It’s perfectly fine to move the zip notch a couple of millimetres in either direction to suit your zip.

Get ready to sew

Preparing the pieces for sewing a fly front zipper.
I like to prepare the pieces before I sew the actual fly.
1. Overlock the fronts – you should still be able to see the zip notch beneath the overlocking.
2. Interface the fly facing with some firm-ish interfacing (fusible or woven), then overlock the long curved edge.
3. Sew the bottom of the fly shield with a 6mm seam allowance, turn through to the right side, then overlock the long sides together (see below).
Sewing the fly shield in preparation for a fly front zipper.
This is what I mean with the fly shield – sew the bottom with a 6mm seam allowance.
Then turn it through to the right side, press, and overlock the long sides together.

Step 2 Sew the crotch seam

Sewing the crotch seam.
Put the fronts right sides together and sew the crotch seam, below the zip notch.
I like to sew two rows of stitching on top of each other, for strength. I stop a bit short of the inseam, so I can sew the inside leg seam later.

Step 3 Sew the facing on

Sewing the facing on a fly front.
Sew the long straight side of the facing onto the front. Take a 1.5cm seam allowance, and finish exactly at the top of the crotch seam (where I’m pointing).
Sometimes, if the fabric is very thick, I’ll step the facing 5mm back from the edge of the front to reduce bulk. Which means I’m sewing it on with a 1cm seam on the facing and 1.5cm seam on the front.

Step 4 Press the seam towards the facing

Pressing the fly front facing.
Press the seam. Press everything away from the front.
Understitching the fly front facing.
I forgot to take a photo of this, but edgestitch the facing next to the seam, including through the seam allowance. This will keep the facing folded out of sight.

Step 5 Sew the zip on the facing

Pinning the zip on the fly front facing.
Take the zip and lay it FACE DOWN onto the facing.
Line up the edge of the zip with the seam.
Make sure the bottom stop of the zip is above the crotch seam. You’ll be sewing the zip on the side nearer the overlocking – where I’ve got it pinned.
If your zip is the correct length (unlike mine), you’ll notice that at the top the sides splay out. Stitch the zip on where it lies, ie splayed out.
Sewing the zip on the fly front facing.
Sew the the zip on with two rows of stitching, one next to the zip teeth and the other next to the edge of the zip. You’ll need a zipper foot.
(From memory, this is where I messed up in my sewing exam – I aligned the zip with the overlocking instead of the seam.)

Step 6 Topstitch

Topstitching the front of the fly front zipper.
Topstitch the facing into position, using a zipper foot – see the important note in the next photo.
You’ll be stitching from the bottom of the fly front UP.
Don’t try and stitch from the top down – the fabric will form a bubble at the bottom.
Note that the top layer will want to move forwards as you stitch, so hold your hands each side of the presser foot and try and encourage it backwards.
I sewed mine using topstitching thread. If you do this, don’t backstitch at the beginning – instead, leave long tails to bring to the back and tie off later. (I’ve already tied mine off in this photo.)
Important!  Keep the zip tape clear!
IMPORTANT! It’s crucial that you don’t stitch in the free end of the zip tape, because you’ll need to sew it to the fly shield later. Pin it out of the way and stitch below it.
Also, don’t catch in the other front or its seam allowance.
Using a template to mark the fly front.
Need a topstitching guide? Make one out of cardboard and draw it on with chalk. Mine is 3cm wide.

Step 7 Sew the shield on

Sandwich the other side of the zipper tape between the remaining front and the shield, and sew it with a 6mm seam allowance. I always pin this seam first (on the 6mm seam) and check how it looks on the right side.
Some people like to sew this part in two steps: first they sew the zip to the front, then they sew the shield on.
Here’s another photo of the zipper tape stitched between the remaining front and the shield.
Optional stitching on a fly front.
This is optional, but I always do it. Sew a row of edgestitching next to the seam you’ve just sewn, through the seam allowances too. Stitch down as far as you can towards the bottom of the zip.

Step 8 Two things to finish

Reinforcing the bottom of the fly front zipper.
Sew a triangle, through all the layers, at the bottom of the zip. Look at the hand-drawn overview above for the details of sewing this.
Again, I used topstitching thread for this, and I’ll bring the ends to the back and tie them off.
Btw, please don’t be tempted to omit the triangle in the pursuit of a clean, minimalist aesthetic. Without it (or any sort of reinforcing at the bottom of the fly), there will be stress on the fabric every time the fly is unzipped and it will eventually tear at the bottom point. Can you hear the regretful voice of experience?
Stitching the shield and fly front together at the back of the fly front zipper.
Turn the fly front over, and stitch the shield and facing together. Just sew back and forth for a short way, or sew a bar tack. This keeps the fly front from opening too far when it’s unzipped.

If your zip is too long, like mine, leave the extra length there for now. Shorten it after you’ve sewn the waistband on, making sure the zip pull is on the correct side!


Of course things go wrong in sewing! Here’s some advice from The Dressmaker’s Companion:

The bottom of the fly front doesn’t sit right

Possible solutions:

  • Does it just need a press? Try unpicking the triangular stitching and the bar tack holding the shield, and give it a press.
  • Unpick the whole shield side of the zip. Re-pin this side in position with the fly shield and check before re-sewing.

Why does it happen?

  • The sides of the zip might not be aligned correctly before sewing, or one side might have stretched. Reduce the likelihood by pressing the facing side after topstitching, and pin and check before sewing the second (shield) side. Some fabrics are more prone to this – take extra care on unforgiving, “bouncy” or difficult-to-crease fabrics such as microfibre.
  • Don’t extend the zip into the curved part of the crotch unless you’re using specially made curved pattern pieces (in the olden days, the fly front sometimes extended into the curved part of the front, requiring a curved facing and shield – these in the Met Museum look like they do).


Looking for other zip tutorials? Invisible zips are here, and regular zips are here with a demo video (6mins). How to shorten a metal zip is here.


  1. Michelle on February 15, 2022 at 11:13 pm

    That is the best tutorial for sewing fly fronts! I have been sewing elastic waisted pants to avoid the dreaded fly front. I am going to try it again with the pictures, and save the tutorial on my computer. Thanks Liz!

    • lizhaywood on February 16, 2022 at 12:24 pm

      Thanks Michelle, that is very nice of you to say! I don’t think you are alone with avoiding fly fronts 🙂

  2. Toni on April 1, 2022 at 8:23 am

    Great tutorial, explains and shows the technique very clearly. Thank you!

    • lizhaywood on April 1, 2022 at 9:20 am

      Cheers Toni!

  3. Sathish babu on February 1, 2023 at 10:12 pm

    Very clear tutorial. Thank you so much

    • lizhaywood on February 2, 2023 at 9:25 am

      Many thanks Sathish.

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