Read This Before You Use Plastic Boning for the First Time — Or After You Made a Big Mistake

You found the perfect pattern — a super cute bustier top, or an incredible strapless dress. But in the notions section, there’s something strange: boning. You have no idea what this bizarre substance is or how to use it or where to get it. Or you’ve heard of it — but that’s the steel stuff they put into corsets, right? That’s got to cost a fortune and be so uncomfortable. You’re ready to put the pattern back — or else make it, skip the boning entirely, and hope for the best.

Don’t do it!!

Plastic pre-cased boning — the type the goes in most bras and bustier tops — is cheap and is super easy to work with and to find. They carry it by the yard at JoAnn’s and most sewing stores and you can also find it online, in various sizes. You don’t need any special tools — just your iron and regular scissors will do — and it takes just a few minutes to prepare the boning.

There’s only a few steps to prepare your plastic boning, and they’re super easy!

And if you jumped the gun and started your project without preparing your boning the right way — and now you’re left with a messy piece of fabric that’s sticking out in all the wrong directions — you may be able to fix it.

Let’s dive in!

NOTE: This post covers how to use plastic pre-cased boning. This is the type of boning that will go in something like a bustier top. If your pattern calls for a different type of boning, like rigilene boning or steel boning, you’ll need to follow slightly different steps (and you may need some special tools) to create your garment.

What is dress boning?

Boning is a thin strip of plastic or metal that gets sewn into a garment to either (1) provide support, or (2) give the garment a special sort of structure.

Since you can’t sew directly over plastic or steel, boning needs to be covered with a fabric case before it can be used. Most plastic boning comes pre-cased and ready to use. There’s also a ton of tutorials online about making casing for boning.

What is boning used for in sewing?

Bras, swimsuit tops, and bustier tops usually feature plastic boning to give your chest support. Heavy duty metal boning is usually found in corsets, to shape the entire torso. Sometimes curved boning is used to make things like hoop skirts.

How to Use Boning in Sewing?

The following five steps will give you a detailed look at how to use boning in your sewing projects.

Preparation: How to Prepare Plastic Boning

1. Flattening: How to Flatten Boning

Your plastic pre-cased boning will probably come bent into a round shape. Before you use it, you need to flatten it. This is the most important step to preparing your boning — if you skip it, your garment will be bent into all sorts of strange shapes.

So how do you flatten boning?

To flatten plastic pre-cased boning, you just need an iron.

Put your boning on the ironing board and unroll it. Turn up the iron’s heat.

Use steam. Iron the boning flat.

(The plastic boning won’t melt, as long as the boning is in the fabric casing.)

You might need to go over the boning a few times with the iron, or use more steam. Don’t take the boning out of the casing and try to iron it that way — your plastic will melt!!

That’s it!

Set the flat boning aside until you’re ready to sew it into your project.

2. Placement: Where Does Boning Go in A Dress or Top?

Your pattern will probably say something like “sew in at the seams” if you’re making a bustier top.

That’s exactly what you’re going to do.

First iron your seams open so they lay flat. Then lay your flat boning down on the center of the seam. With tailor’s chalk or pencil, mark the seam length on the boning. Repeat for each seam.

(You may want to cut each piece as you measure it, and lay it down on the appropriate seam, so you don’t lose track of your pieces. See below for cutting instructions.)

3. Cutting: How to Cut Plastic Boning

Cutting your plastic boning is super easy. You don’t need any special tools, just your regular old scissors.

After you lay your boning on the seam of your garment and mark how long you need the piece of boning to be, simply use your scissors and cut the boning to the desired length.

That’s it!

4. Trimming: How to Properly Trim Plastic Boning

Now that all of your boning pieces are cut to the proper length, you’re going to want to trim the plastic part of the boning. This is so the boning fits into your garment properly, without stretching it out or causing the fabric to tear. This will also prevent the boning from poking you while you’re wearing your garment, which is pretty uncomfortable.

Gently push the fabric casing down, so that the plastic tip of the boning is exposed. Next trim off about a centimeter. Use your scissors to cut the corners and give the boning a more rounded shape.

Repeat this process on both ends of every piece of boning.

Sewing: How to Sew Plastic Boning

1. How to Sew Plastic Boning into A Garment

Congratulations! You’re finally ready to sew the boning into your garment.

Sewing boning into a garment is easier than you might imagine.

First, pin down each of your trimmed pieces to the appropriate seams. Then bring your garment over to your sewing machine.

You’re going to sew the boning along the fabric casing. You’re going to sew each piece vertically, alongside the plastic inside, and also horizontally, across the piece of fabric at the top. (This is why we trimmed our boning: So that when we’re sewing across the top, we don’t need to sew across the actual plastic.)

You can use your regular needle and thread to so the boning in.

Be sure to sew very straight, and avoid sewing over the plastic with your machine. If you do sew over the plastic, it’s not the end of the world. Your machine won’t break. Your needle probably won’t even break. However, if you do this repeatedly, you may have some problems with your machine and needle in the future, so try the best that you can only sew the fabric.

That’s it!

Now the only thing that’s left to do is to try on and enjoy your beautiful, supportive garment!

Boning Troubles: What to Do If You Sewed Your Boning in Curved

If you’re looking at this post retrospectively (after you already sewed some seriously curved, unironed boning and your garment is looking seriously lumpy and misshapen), don’t worry too much! You might be able to salvage your work.

In fact, the very first time that I used boning, I had no idea that you needed to iron it.

I was making the cutest tie-front top, using McCall’s M7937.

I sewed way too much boning and each of my seams, and it was totally curved. The entire thing turned out as a serious mess. I thought the garment was unwearable, and I was about to throw it away, much to my dismay, since I used the cutest turquoise daisy-printed fabric.

In a last-ditch effort, I decided to try to iron the whole thing.

It worked! Kind of. I used a lot of steam (I’m talking a LOT). And I ironed the front and the back, multiple times. Eventually, the boning lay flat enough for me to be able to wear the top. There was just one problem. Now, since the boning was flat where it had once been curved, it was way too long for the garment. It really stretched out the fabric, and wherever there was boning, there was also an awkward bit of fabric that seemed to stand up on its own.

I did the best that I could to trim away some of the boning from inside of the casing, though since I already sewed it down, this was impossible in some places.

At the end of the day, it wasn’t my best work, but it was something I was able to wear!

If you find yourself in the same boat, I do recommend trying to iron the garment the best that you can, and then trim away whatever boning you are able to. It may not be your very best garment, but at least you won’t have to scrap the whole entire project. And you’ll never forget flatten your boning again!