Swimwear Elastic: Everything You Need to Know

One of the most common categories of questions when it comes to sewing swimwear is elastic. What is it, how do you sew it, why is it such a pain sometimes? In this post we're aiming to answer every question you might have about elastic for DIY swimwear.

On YouTube we'll be doing a three part series that answers these questions and more. If you prefer to watch the video, you can find them below.

Part 1: The Most Common Questions + Before You Sew

Part 2: While You Sew + Demo

Part 3: Troubleshooting

The most commonly asked questions

Do you need elastic?

I’m going to answer this question from two different views, because honestly it depends.

First, the “proper” sewing view. Technically speaking, you should always use elastic in your swimwear. This is because the elastic serves an important purpose, and that purpose is helping the garment keep its shape. The actual fabric will stretch over time, but it’s the elastic that keeps everything in place. Elastic also helps the garment sit nice and flat so seams don’t roll over. On top of all that, having elastic in your swimwear looks and feels more professional, so if you’re selling swimwear that’s definitely something to consider.

Now I’ll discuss circumstances where you don’t “need” elastic. There are a few common complaints on why people don’t want to use elastic, and honestly it’s your choice. Sure, technically speaking using elastic is the correct way. However, at the end of the day it’s your choice.

Some people don’t like the feeling of elastic. It can feel constricting and some people just prefer a looser fit. There are others who don’t have the means to get elastic, usually because they can’t find any that ships to their country. Then there’s the people who aren’t worried about being proper quite yet, they just want to sew a bikini!

So I say just do what works for your situation!

What width of elastic should you use?

This is a little bit of personal choice and a little bit of “depends what you’re doing”

I use ¼” elastic for pretty much everything

If you'd like added support you can use 3/8”. I only really use 1” for bands, extra supportive straps, or for thick straps just for stylistic choices.

I’d say if you had to choose one size of elastic for every project, I’d go for ¼”!

What kind of elastic should you use? rubber, braided, or clear?

This is going to be another answer with a technically correct answer, but another “do what you want” situation.

Rubber elastic is the best elastic for swimwear. It holds up the best in terms of tension, plus it’s resistant to chlorine, salt water, UV, and sun tan oils.

Everything I’ve come to learn has said that braided elastic doesn’t hold the same tension as rubber, and it’s not suitable for swimwear purposes. However, I like to buy swimwear from big brands and take them apart to see how the manufacturer constructed the piece. And lately I’ve been seeing a lot of braided elastic! So I don’t know anything about where to find it but apparently there is braided elastic out there these days that can work for swimwear.

Finally, clear elastic. People really like this stuff, but unfortunately out of all three it seems to be the one to break down the quickest, especially when it comes to UV

So bottom line, rubber elastic is the best I’ve found, but if you do come across braided that’s meant for swimwear then go for it

Part 1: Before You Sew

What type of needle and thread should you use to sew elastic?

For thread you can use regular polyester thread, just make sure it’s high quality.

With cheap thread you really do get what you pay for, so if you’re having issues with your machine then it’s possible cheap thread could be the reason

For needles I’d recommend using either ballpoint or stretch needles. I’ve read that stretch needles are the best specifically for elastic!

Make sure you change out your needles after 24 hours of using them or whenever you start to notice problems with your stitching.

Where to buy swimwear elastic

This depends on whether you want to buy a bunch of elastic or just a little.

First and foremost, we sell elastic! It is made in the USA and we have quantities from 10 yards all the way up to 1,000 yards.

Get elastic here

There are of course other places you can get elastic from, just make sure if you're buying rubber elastic that it's apparel grade!

Part 2: While You Sew

Do you stretch while sewing? How much?

I don’t stretch at all while sewing.

There’s a good argument to stretch the elastic in order to make a more snug fit, and most non-reversibles use this technique. However, with reversibles it’s a different issue

For one, if you stretch the elastic then the garment won’t lay flat, which maybe you don’t care about and that’s fine. But for aesthetic purposes you typically don’t see a lot of scrunched up swimsuits hanging on a rack at the store.

And the other reason why I don’t stretch is because I don’t like the feeling of tight elastic. That’s just personal preference though, so stretch the elastic if you want to!

As far as what percentage to stretch the elastic, it depends on the garment and your personal preferences. From what I’ve seen, a reduction of 2-3% is appropriate. So you’d measure the length of the seam, multiply it by 0.02, then subtract that number from the length of the seam to calculate the length of your elastic.

How much elastic do you need?

It depends on the style, but typically I use anywhere from 2 yards to 10 if it’s a super strappy strappy style.

It’s good to keep at least 10 yards on hand, but if you do a lot of sewing I suggest keeping much more than that on hand.

Edgewater’s sister company Swimwear Notions USA sells elastic by the pound and I usually keep a 1 lb box at all times.

Does the stitch have to cover the elastic fully?

From my knowledge, not necessarily. This is all anecdotal though, so I could very easily be wrong on this.

But from pieces I’ve made and swimsuits I’ve purchased I’ve seen some that cover the seam fully and some that don’t. The ones that don’t cover the seam fully are usually because wider elastic is being used like 3/8”. And those are fine! In some fabric you can see the unsewn part of the elastic but it's not super noticeable.

But again this is just anecdotal evidence so take it with a grain of salt.

Does the elastic sit better on one side versus another in reversibles?

Yes, I’ve found that elastic sits better on the “dominant” side, so whichever print you want to be the primary one. But honestly in my reversibles there isn’t much peeking over even on the non-dominant side.

Do you need to adjust tension when switching from sewing with versus without elastic?

For some machines yes, for some machines no.

My serger has automatic tension so I’m never changing it unless I’m switching from swimwear to an entirely different fabric. But machines that do have tension options will often need an adjustment when switching from sewing fabric to sewing elastic. And not just that- Some machines will need a change in tension switching from one fabric to one even slightly different.

It just depends on your machine!

When do you stop sewing elastic as you're getting close to a seam?

This is a controversial question and many of you might not like my answer. Sew the elastic all the way to the end of the seam!

I used to cut the elastic short and taper it but when you do that you can sometimes see it when the piece is finished. Plus, if the elastic falls short then it’s not actually holding the tension it’s intended to. Instead, the part of the seam without elastic is holding that tension too, which is a big no no and could wear down and stretch out that seam over time.

So I sew my elastic all the way to the edge, then I trim it after I’ve sewn the sides or straps or whatever it is.

Cutting it short/tapering is in an attempt to prevent bulkiness at the seam, but honestly if you do a good job trimming it still prevents that bulk pretty well. Not 100% but I think the trade off is worth it.

Puncturing rubber elastic- how many times is too many?

If you sew over rubber elastic once and you have to go back and redo, I’d highly recommend moving on to a fresh piece of elastic.

Needle punctures mess with the structural integrity of the elastic and I wouldn’t gamble with it. If you’re just making pieces for yourself and you’re trying to conserve elastic then maybeeeee use it again, but the proper thing to do would get some fresh elastic.

Do you need an elastic foot

Not necessarily! I didn’t have an elastic foot for years and I got by just fine

If you don’t have a foot you’ll just break up the process into two steps- first sewing the fabric, and then going back and sewing the elastic.

How do you sew elastic flat?

The theory is that you want even tension on both the fabric and the elastic. If one of those is pulled even just slightly that can cause waves or bunching. If you’re using an elastic foot it can be a lot easier to find the right tension!

Also, you should not only pay attention to pulling as the fabric and elastic are feeding into the machine, but you should also be careful about pulling it too much or too little out of back of the machine.

Even if you think you’re doing everything right, there’s a good chance that the problems you’re having have to do with your machine.

The feed dogs are what feed the fabric through, and if those are pulling the fabric faster or slower than the elastic is feeding then that can be the root of your issues. I had this problem before I had an elastic foot, and what helped me was keeping my left hand holding the back of the garment as it goes out of the machine. With the left hand I’d gently guide the fabric so it didn’t rely on the feed dogs so heavily.

Tips for sewing elastic on to straps

Straps can be especially challenging because they’re so thin, so here are some tips!

First, use a basting stitch. I’ve been sewing for years and I still do a basting stitch every time. Having the fabric sewn together is an invaluable tool because then you can focus just on the elastic application.

Second, leave extra seam allowance. Some machines will suck up fabric pretty easily, so having extra allowance can help to prevent that from happening.

As far as bunching or waviness goes, straps can be the hardest. So I recommend using the tips I talked about on how to apply elastic flat as well!

How to apply elastic without an elastic foot 13:03

How to apply elastic with a regular sewing machine 17:59