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How to Sew Elastic into Swimwear

By Allie

Allie is the co-founder of Indiesew and creator of all things pretty on the site. Follow Allie and receive other Indiesew updates by subscribing to the blog.

Indiesew Tutorials | How to Sew Elastic into Swimwear
Sewing your own swimwear is daunting to some sewists, and a total thrill to others. And for most, it’s often a completely new experience. Sewing with ultra stretchy fabric, linings, clasps, and swimwear elastic is nothing like sewing up a flowy summer blouse. In fact, it’s quite the opposite. But sewing your own bathing suit doesn’t have to be scary.
First, it’s important to understand that handmade swimwear will not look like your ready-to-wear bikini, unless you own a lot of fancy equipment. The home sewist, using just a sewing machine, won’t sew the perfect cover stitching that an industrial sewing machine can achieve. But that’s okay! If you enter into your first swimwear project with this mindset, you’ll be less disappointed when your elastic looks a little wavy and wonky. Like most new skills, it will take a few attempts to get it looking just how you want.
Second, sewing swimwear is incredibly forgiving. I say this because swimsuits are made entirely of very stretchy materials. By nature, those materials will lay flat and look much nicer when stretched over hips and torsos, than when lying flat on your cutting table. If your elastic isn’t stretched nearly enough in areas, or your stitching is a little crooked, chances are no one will be able to tell when you’re wearing the item. So don’t be afraid to make mistakes on your first bathing suit. It’s going to happen, and it will likely still be very wearable. 
Today I’m covering a topic that may be the most difficult part of sewing your own swimwear, but it’s one that newbies can easily master in a short amount of time. Today, I’m sewing elastic into my handmade swimming suit bottoms. I’ll be demonstrating this technique on the Nautilus Swimsuit, sewn in the Olive Nylon Lycra Swimwear Fabric.  
For this tutorial you’ll need swimwear elastic. Check the elastic requirements in your sewing pattern for the correct length. I use Dritz 1/4 inch Cotton Swimwear Elastic that can be found at your local big box sewing store. If you’re sewing a lot of swimwear, you might consider buying this elastic in bulk, found here.  
Swimwear Sewing Supplies | Dritz Swimwear Elastic
I recommend serging or basting your swimwear fabric and lining together before inserting your elastic. I find it difficult to manage two layers of sometimes slippery fabric and apply tension to the elastic at the same time.
Note: Some swimwear patterns draft the lining pattern piece smaller than the exterior pattern piece to avoid bulk in the elastic seam. In this case, do not serge your lining and exterior pattern pieces together. Instead, follow the instructions of the pattern.

The Safety Pin Method

I discovered the safety pin method when teaching an undies sewing classes at Fancy Tiger Crafts. For me, it’s a foolproof way to start your elastic insertion.  

Attach a large safety pin to the short end of your elastic. Pin your elastic to the wrong side of the fabric at the center back (or where the pattern instructs) of your swimwear, leaving about two inches of an elastic/safety pin tail on one end. Place the elastic about 1/16” in from the outer edge of the swimwear. This will completely conceal your elastic once you fold it over. Blog | Safety Pin Method for Swimwear Elastic
At your sewing machine, change your stitch settings to a long and narrow zig-zag stitch. My default zig-zag settings for stretch garments are shown below.
Zig Zag Stitch Settings | Sewing Swimwear
Now, center your presser foot over the elastic near the pin, with the safety pin behind the presser foot. Keep your presser foot raised and lower your needle into the elastic with your hand wheel.
Lower Needle into Elastic | Sew Your Own Bathing Suit
Lower your presser foot, grasp the safety pin with one hand while you start slowly sewing a few stitches. Then, apply a bit of tension to the elastic with your other hand as you continue to sew the elastic to the swimwear.
Sew Elastic Into Swimsuit | Indiesew Sewing Tutorial
You might be wondering, what’s the purpose of the safety pin tail? Without an elastic end to gently tug through the sewing machine, your presser foot and needle can often get stuck on your elastic, especially when starting to sew. This creates an unsightly mess of zig-zag stitches and will also create an area of your swimwear where the elastic will have no tension. 



Sew Your Elastic Onto Your Swimwear

Continue to sew your elastic onto your swimwear in the same manner, adjusting the amount you stretch the elastic as you sew different areas of the swimsuit. Here’s the reference I use:  

  • On straight edges, like waistbands and straps, apply a small amount of tension as the elastic feeds through the machine. I simply place the elastic between my thumb and forefinger and let it feed through with the speed of the sewing machine. If you don’t apply enough tension on straight edges, it won’t ruin your swimwear. Your elastic edges may appear wavy, but when the item is worn that effect will disappear.
  • On concave edges, like around the crotch or under the armpit, I apply the same amount of tension as I would on straight edges. Again, if you don’t apply enough tension here, it won’t ruin your swimwear. 
  • On convex edges (shown below), like around butt cheeks and under the bust, apply a significant amount of tension to the elastic. I stretch the elastic to approximately 70% of its maximum stretch. If too little stretch is applied to the elastic, the swimwear won’t cup properly to your butt or under your bust. This can result in constant wedgies and the occasional nip slip. No fun.
Handmade Swimwear | Sew Elastic Around Leg Opening
If you’re brand new to sewing swimwear, I recommend following the sewing pattern’s length requirements for elastic around the various edges of your swimwear. Or, for a slightly different method of attaching swimwear elastic, watch SeamstressErin Design's video. Experiment with these techniques and don’t worry too much if you don’t get it exactly right. Like I said, swimwear is forgiving. With more experience, you’ll be able to attach swimwear elastic by feel.
As you approach the end of your swimwear edge, trim off the elastic/safety pin tail. Then overlap the elastic ends by roughly 1/2” and backstitch at the end.  
Clip Excess Elastic and Sew Down | Indiesew Blog



Fold Over and Topstitch the Elastic

Now that your elastic is sewn onto the wrong side of the swimwear, you're ready to finish the edge. Fold the elastic over to the wrong side of the fabric. With the same stretch stitch settings, place the swimwear under your presser foot with the right side of the fabric facing you. 

Topstitch along the edge of the swimwear, feeding the swimwear through the machine at a consistent rate. Be sure to stretch the fabric away from the folded edge (perpendicularly) as you sew. This will keep the elastic edges completely smooth.  

Topstitch Elastic with Stretch Stitch
This is what your finished seams should look like:
Finished Topstitching | Nautilus Swimsuit Bottoms



Common Mistakes

Even after sewing several bathing suits, my elastic insertion is not always perfect. Here are some common issues that I’ve had while sewing swimwear elastic and what causes them. 

If you notice small diagonal wrinkles in the finished edge of your swimwear (shown below), you likely stretched your swimwear fabric at an angle (not perpendicularly) from the edge of the fabric while you topstitched. Leaving your needle down, lifting your presser foot, and repositioning the excess swimwear fabric away from the edge while topstitching will fix this problem.  

Fabric Stretched at Angle to Folded Edge | Common Swimwear Mistakes
If you notice extra fabric wrinkled at the edge of the elastic (shown below), you likely did not stretch the swimwear fabric away from the edge enough while topstitching. 
Excess Fabric at Folded Edge | Sew Your Own Swimwear
If you have extra materials, I recommend practicing your swimwear elastic technique on a few scraps. It will help you to understand the mechanics of this technique and also find out how difficult your swimwear fabric might be to work with. 
We’ll be back later this week with a roundup of our favorite places to source swimwear materials, plus an exclusive coupon code just for Indiesew readers!
Don’t forget to save 20% on all swimwear sewing patterns using coupon code SWIM2015 at checkout until 10 p.m. MDT on August 9. Also, there are just a few yards left of our swimwear fabrics. Get yours while they’re still available!
Happy swimwear sewing!

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For smooth elastic finishes on your handmade swimwear, try the safety pin method! |

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