Sewing zippers can be daunting, and sewing a fly zipper can be even more so due to all the pieces and metal teeth. I am here to walk you through the steps and give you some tips for sewing a fly zipper that will make this experience enjoyable instead!
Currently, many fly tutorials are floating around online as there are more and more pants and jeans patterns available that use this technique. There are even jeans-specific hardware kits that include everything you would need to finish a pair of jeans or workwear garment. Our favorites are from Core Fabrics and Kylie and the Machine. 
Now for the pieces that make up the fly. 
First, you have your front pant pieces. For this section, I will be referring to the RIGHT FRONT and LEFT FRONT as if you were wearing pants.
Next, you have the fly facing (the curved piece) and the fly shield (the rectangle piece). The reason why we have the fly-facing piece patterned as a separate piece rather than an extension of the front is so that you have the option to use a different fabric for the facing.
If you are sewing with a heavier fabric - or want to have an extra pop of color or detail to your pants - it is recommended to cut your fly facing out of the same material you used for your pocket lining. For heavier fabrics, this is best so that the fly is easier to sew and is not too bulky when sewing the front seat seam together. Eventually, all of these pieces will intersect at the bottom of the zipper. 


Fold the fly shield right sides together, matching the long edges. Stitch along the bottom short edge at 5/8" (1.5 cm).
Turn the fly shield right side out. Use a point-turner for the bottom corner. 
Finish the long edges of the fly shield together.
Finish the curved and long straight edges of the fly facing. 


Finish the center front edges of the front pieces.
Match the front pieces' right sides together at the center front. Sew the front seat seam from the inseam up to the zipper notch, finishing the stitch line 1/4" (6 mm) past the zipper notch. 
Clip into the seam allowances at the zipper notch. Clip at an angle up to
the end of the stitch line. Do not clip into the stitch line.


With the right sides together, match the fly facing to the LEFT FRONT at the center front. Stitch together with a 5/8" (1.5 cm) seam allowance.
First press the fly facing and seam allowances away from the center front along the seam. Trim and grade the seam allowances if needed.
Press the fly facing to the wrong side of the left front. 
Press the center front edge of the RIGHT FRONT to the wrong side at 3/8" (9 mm). 
Press the front seam allowances together towards the LEFT FRONT. Using topstitching thread, edgestitch, and topstitch along the seat seam catching the seam allowances underneath. Stop stitching about 1" (2.5 cm) down from the fly opening.
For me, a notion that is a game-changer for easily installing zippers is wash away wonder tape. Wonder tape acts like double-sided tape and is perfect for keeping zippers in place. It is fine to use pins when sewing in zippers, however, pins can sometimes create bubbles in the fabric and may not keep the zipper flat against the fabric causing it to move out of place when sewing. Wonder tape can be found at most fabric stores and online.
We will first be sewing the right-hand side of the zipper to the front. For this part position your front pieces and zipper with the WRONG sides facing up.
Place a strip of wonder tape, sticky side down, to the folded back edge of the RIGHT FRONT. 
Peel the paper off of the wonder tape to reveal another sticky side. 
With your zipper's wrong side facing up, match the right-hand side of the zipper to the wonder tape. Place the zipper so that the zipper tape's edge aligns with the center front's finished edge. Align the bottom edge of the zipper with the zipper notch and bottom of the fly facing. Using your finger, press along the zipper so that it sticks to the wonder tape. It is ok if your zipper extends past the waist edge, we will cut the zipper to the correct length in later steps.
Flip your front pieces and zipper to be right sides facing up. Fold the LEFT FRONT out of the way so it is easy to see the RIGHT FRONT and zipper. 
Using a zipper foot, edgestitch along the folded front edge, through all layers, to secure the zipper. 
Now, match both fronts right sides together.  
With the pieces right sides together, you’ll see the RIGHT FRONT edge and zipper will extend past the LEFT FRONT about 1/4" (6 mm).
Unfold the fly facing so it is away from the left front. Place a pin at the waistline, through both front pieces to keep them in pace. 
The fly shield will extend past the zipper and cover it completely. We will now sew the zipper to the fly shield.
Fold the fly shield away from the zipper for just a moment to put wash-away tape on the left-hand side of the zipper.
First place the sticky side down on the zipper and using your finger press the tape to the zipper. Peel off the paper backing to reveal another sticky side.
Fold the fly facing back over the zipper. Using your finger, press the fly facing to the zipper and tape.
Using a zipper foot, stitch the zipper to the fly facing. Make one row of stitching close to the zipper teeth. Make a second row of stitching right along the edge of the zipper tape.
Open up the front pieces and position them with the right sides facing up. Check how the center front and fly pieces are laying. Ensure there are no bubbles or puckers and the waistlines are even. 
Next, mark a J-stitch line on the LEFT FRONT using the pattern template. Pin the fly facing to the LEFT FRONT along the curved edges.
Using topstitching thread, make one row of stitching following your j-stitch marking, through all layers. Be careful at the bottom of the j-stitch that you are not sewing over any metal zipper teeth or the zipper stop. If your j-stitch line goes into your zipper, just redo the lower part of the j-stitch so it curves below the zipper stop. 
Make a second row of stitching 1/4" (6 mm) away from the first row of stitching. 


Open the zipper all the way. Using a pliers tool remove one or two metal zipper teeth at the waistline edge and also 5/8" (1.5 cm) down from the waistline edge.
Using your paper scissors cut the zipper tape at the waistline.
On the RIGHT FRONT create a new zipper stop where you removed the metal zipper teeth. If you are using a zipper kit, sometimes they come with zipper stoppers that you can clamp onto the zipper tape. If you don't have extra zipper stops, you can simply stitch over the zipper tape, backstitching several times to create a zipper stop. Even though you created a zipper stop, it would be best to not fully zip the zipper until you attach the waistband in later steps to make sure the zipper pull doesn't come off or get stuck.


Position your fronts and zipper to be the wrong sides facing up. 
Match the finished edge of the fly shield to the zipper edge on the RIGHT FRONT. Match the raw short edge of the shield to the waistline.
The fly shield should cover the entire portion of the zipper and fly-facing. 
It may be helpful to use wash-away tape here as well instead of pins as the fly facing may be too bulky for pins.
If you haven't yet, open your zipper. Using your zipper foot, stitch over the stitch line from sewing the zipper to attach the fly shield. Start at the waistline and down. You may not be able to stitch to the bottom of the zipper and that is ok. We will finish the bottom part of the shield in the next steps.
Using topstitching thread, finish the front seat seam stitches, having them go all the way up the seat seam to meet the J-stitches. You might stitch a little bit over the bottom of the fly shield and that is ok.
Make a horizontal bar tack through all layers (front, fly facing, fly shield) at the end of the j-stitch. Optional: make another bar tack through all layers right where the j-stitch begins to curve.
You have now completed the fly zipper! Way to go!
July 09, 2023 — Adrianna Aguirre