Posted by: michelenel | 17 August, 2015

Learn how to insert a fly front zip….

After making a couple of pairs of tailored trousers, it was fairly obvious that the instructions in most patterns were not that great for a newer sewer.  When I taught my son to sew his first pair of trousers he found it very confusing and so I decided to create a step by step photo tutorial which we could laminate and hang up in Sewing HQ for easy reference.

I had the opportunity to create the tutorial whilst making a pair of trousers for him last week.  After typing it up I asked him to use the instructions to insert a fly front zip in his latest pair of tailored trousers.  He found it so much easier and after a few minor amendments here is the result….

How to insert a fly front zip


Using the instructions in patterns is sometimes confusing, but I hope that this little tutorial will give you the confidence to give it a try. This is a freehand method that does not use the pattern pieces included with the pattern and I believe this makes it more versatile and gives you a better understanding of the technique and therefore allows you to make your own modifications later on – you don’t really get this level of understanding by simply following pattern instructions.


  • Practice on some scraps and insert a fly front zip.
  • Test out your newly acquired skills by adding a fly front zip to a pair of trousers or a skirt.
  • Learn to Press, Press and Press again – at every step of the process. Press newly sewn seams to make the stitches ‘sink’ into the material and then press open or to the side. Where necessary, use your pressing clapper to really set your seams.

Note: Where I refer to the right or left side, this is from the perspective of the garment is being worn. Add sticky dots or chalk to clearly mark the right side of your fabric.


1.  Select your zip. Choose a zip that is the length of the front fly opening from the cut edge of the waistband to about 2.5cm/1inch above the curve of the crotch. My example is 19cm (and this should include the zipper tape).

zip 1

2.  The Outer Fly (OF)

a.  Cut 1 piece for the OF from main fabric and 1 from interfacing

b.  Cut the main fabric piece – Length of zip (including tape) 19cm (replace with your zip measurement) x Width 7cm

zip 2

c.  Round one corner of the rectangle in a gentle arc – RS up and cut arc on the left-hand (LH) side

zip 3

d.  Cut the interfacing piece to match your OF

zip 4

e.  Fuse the interfacing to the wrong side (WS) of the OF

f.  Neaten the straight edge and rounded edge (not the top edge as this is enclosed in the waistband)

zip 5

g.  Press

3.  The Inner Fly (IF)

a.  Cut 1 piece from main fabric and 1 piece from lining fabric

b.  Cut the main fabric piece using the OF as a template (RS facing WS) BUT increase its size by adding on 1cm all round the curved side for a seam allowance

zip 6

c.  Cut the lining fabric to match the OF from step 3b

d.  Stitch the fabric and lining right sides together (RS) round the curved side of the OF

e.  Trim and clip if necessary (I used an overlocker so didn’t need to trim or clip)

f.  Turn RS out and press flat

g.  Neaten the straight edge

h.  Press

4.  Join Front Trouser Pieces

a.  Using your 2 front pattern pieces or 2 scraps cut with a curve to represent the crotch RS together

b.  Align your zip along the straight edge of the front seams, with the top of the zipper tape at the waistband edge. Make a mark on your seam line where the zip stop ends (not the tape)

zip 1

c.  Stitch the front pieces RS together from the mark (step 4b) to about 3cm away from the inner leg seam (this gets closed up later on in the process)

zip 8

5.  Adding the Outer Fly to the Left Front

a.  Stitch the OF to the left front (LF) pattern piece aligning the straight edges and RS together – stitch from the stitches near the crotch (where you marked the zip stop) to the waistband using a 1cm seam allowance

zip 9

zip 10

zip 11

b.  Press seams toward the fly front

zip 12

c.  Topstitch along the fly front ON the fly front

zip 13a zip 13b

d.  Fold fly under front of trousers and press (note: if you have used thick fabric or many layers, such as mine which has the pocket extending all the way to the fly front, then you may want to grade some of the fabric away before turning under).

zip 14

6.  Attach the Zip to the Inner Fly Panel

a.  Attach the zip to the straight edge of the IF panel – align the LH side of the zipper tape to the LH side of the IF panel with the top of the zipper tape at the raw edge; pin or tape this down on the right-hand (RH) side. Stitch about 3mm away from the zipper teeth starting at the zip stop; go to about half way, stop with needle down, raise your presser foot and carefully open the zip so the zip tab is now at the zip stop, lower the presser foot and continue to stitch to the end.

zip 15

zip 6

zip 16

7.  Adding the Inner Fly to the Right Front

a.  Press the right front from the waistband down to the crotch with a diminishing seam allowance – starting at the waistband fold back 1.5cm and gradually reduce this towards the inner leg seam so that you have the seam from the zip stop to the inner seam folded over only just in half (about 6mm). This sets back your zip at the bottom edge so it is hidden inside the fly.

zip 17 zip 18

b.  Place the zip and IF panel and pin it under the RF along the newly pressed seam allowance. Fold OF out of the way.

zip 19

c.  Top stitch about 3mm from the zipper teeth from just below the zip stop to the waistband edge.

zip 20

d.  Flip the trousers over so the RS is up and lay the LF fly over the RF fly (as it would look when completed) and tape (or baste) along the open edge to keep it in place. Now make absolutely sure everything is lying flat and neat.

zip 21

e.  Flip it back over to the wrong side, fold the UF out of the way (it will expose the OF and the zip) and insert a few pins along the LH zipper tape to keep it in place. Do NOT pin it to the trouser front – only to the OF.

zip 22

f.  Flip back to RS, remove the tape and check that everything is neat and flat and that the zip is properly hidden inside the fly.

g.  Stitch the zipper tape to the OF from the zip stop to the waistband. Start with zip closed and open it when you have stitch half way up the tape, then continue to end.

zip 23

h.  Check that your zip works properly and is correctly hidden behind the fly.

zip 24

i.  On the RS of the trousers, re-tape the fly closed along the fly front.

j.  Flip over to the WS, fold the IF back out of the way. Pin the OF to the front pattern piece near the zipper tape.

zip 25

k.  Fold the IF back over the OF and zip and check that it neatly covers the entire fly.

zip 26

l.  Top stitch from just below the zip stop to the waistband to create the classic arc of stitches visible on the outside of a fly. The top stitching goes through all of the layers. If you are not confident you can sew this in a nice arc shape freehand, make your lines with chalk or pen beforehand.

zip 27a

m.  Trim off the tail ends of your zipper tape if they stick out from the IF.

n.  Flip the trousers over to the RS and through all the layers pin the trousers, OF and IF at the end of the curve of top-stitching.

zip 28

zip 29

o.  Flip the LF back towards you to expose the OF and IF. Pin through the rounded end of the OF and IF and stitch a little bar-tack or back/forward to keep them together.

zip 30

p.  Turn back to the RS and finish off the top-stitching on the front of the trousers from where you placed your pin in step ‘o’ – start at the crotch seam (put your needle down into the seam) and top-stitch toward the previous top-stitching and either reverse back towards the crotch seam or needle down and turn and sew back over the previous stitches towards the crotch – repeat. This will join up the top-stitching and secure the base of the zip at the same time.

zip 31

….and that’s all there is to it!  Phew!

If you prefer you can follow this link to download the PDF and print it off……

Insert a Fly Zip

I really hope that this comes in handy for you and that it helps you to achieve beautiful garments along the way.

Good luck and happy sewing.


  1. Thank you for sharing your fab tutorial – you make it look so straight forward 😀

    • My absolute pleasure. Let me know what you think if you ever try it. 😊

      • I’m sure I will, it’s a while since I made any trousers, bit with winter just around the corner they’re nearing the top of the to do list! 😀

  2. Pinned for reference later. Your Project Management skills still shining through. Please share more tutorials if you have the time, I know they’ll be useful for me and many other home sewers.

    • You are too kind. I am hoping to add a few over time. Welt pockets next maybe. 😄

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