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Bra Underwires 101: A Basic Guide

Note: This post contains nudity.

Bra Underwire Patent via Wikimedia Commons

Bra Underwire Patent via Wikimedia Commons

Today's guest post is by Lyzzy Beswick. Hailing from the beautiful Derbyshire Peak District, Lyzzy is a DeMonfort Contour and NTU Fashion Management Graduate.  She currently works as a freelance technical lingerie designer for KissMeDeadly, Augustine London and several other independent brands. Her obsessions include pole dancing, antique lingerie, rock music, Smart cars and green tea. Lyzzy's favorite lingerie brands (besides those she designs for!) are Carine Gilson, Princesse Tam Tam, Ava Corsetry, La Perla, and Shell Belle Couture. Lyzzy and Ventilated Corset Pic

Most modern bras are underwired, but how much do you know about them? Why are underwires in our bras? What are the different shapes and types of underwires, and what does each one do? And what do you need to look for when buying an underwired bra... or even when making one?

What are underwires?

In 1931, Helen Pons patented a U-shaped wire to be worn flat against the chest wall, a very similar design to the underwires we know today. Though U-shaped wires and even O-shaped wired (which means the wire went all the way around the breast!) bras were developed, soft triangle bras, slips, and camisoles remained more popular during the 1930s and 40s, with underwired bra only taking off in the 1950s. Even then, many bras had overwires instead, which provided no shaping or support, just a fashionable silhouette.


Kiss Me Deadly Overwire Bra

An underwire is an artificial, idealised, regularised form of the breast root. The root of the breast is where the breast joins the body. In my days as a Contour fashion student, we all got very hands on with this, drawing around our breasts with medical markers, green eyeliner pens and anything else non-toxic we had on hand! Then we would take measurements, photos, and draw breast root traces with a flexicurve. It may sound ridiculous, but the point is to study and understand how the natural breast root shape looks and how underwires affect it.

Taking a breast root trace with flexi curve

Taking a breast root trace using a flexicurve.

Natural breast root shapes vary greatly even for breasts that are in the right bra size, so if you are struggling to get a good bra fit, taking a breast root trace can be helpful with comparing wire shapes to your body, so you can decide which bra has a more sympathetic fit for you.

Breast Root Trace

The difference between a natural breast root and same sized underwire.

Underwires are narrower than our breasts, but once put into a bra, the fabric sides of the bra pull them out. The sides and the cup of a bra form a cantilever which lifts the breast upwards from the base – which is why you shouldn’t need the straps of your bra for much support!

Most women have one breast larger than the other, but wires, of course, are identical, providing a more symmetrical base. The main function of the underwire is to push the breast into a certain shape, a bit like putting playdough through a mould! The breast is contained inside the wire outline and the breast volume pushed into in a chosen direction to give a certain appearance or fashion shape for the specific type of bra. Wires provide support in combination with the cradle and cup of the bra. Different wire types are intended to provide different shapes.

Underwires can be plastic or metal. Plastic has a tendency to snap and so is generally only used in cheap mass-produced underwear, or in swimwear to avoid rusting. The majority of underwires are carbonised steel with an outer coating of nylon and an extra coating on the ends.

The 3 Main Types of Underwires:

There are surprisingly few key types of underwire shape, but many subtle variations are found within each type. The main ones are:

Common wire shapes

Balconette/Day bra
This is a J-shaped wire intended for all day wear without any especial fashion aspects. In training, we call this a Daybra. That’s just a bit of industry shorthand for a daily wear bra, not a brand or term most people would  know! A Daybra wire is shorter in length than the other wire types, and so has a greater difference between the height of its two ends. They are used for balcony and balconette bras and fuller cup/everyday bras, respectively, and are a shape quite sympathetic to many women’s natural breast root.

Also known as a ‘rocker’ wire, these are banana shaped. Some are slightly more hooked at the centre front end and others are just like the curve of a banana. These wires are put into the bra at a sharp tilt and are primarily used in push-up/plunge and infrequently in demi and very low balconette bras. They are designed to push the breast upwards and towards the centre front, giving more prominent cleavage and deeper neckline.

These are a deep U-shape wire, and are nearly the same height at the side and centre front ends. The principle here is that the breast falls into the deep U, where it will be contained completely, supported from underneath, and projected forwards. A strapless bra needs to grip, contain, and constrain the breast more in order to both provide support and stay in place. For a smaller cup size range, I occasionally select a balconette wire if it suits the style required better.

A note for D+ Cups
Nowadays, a good bra wire will tend to be oval in cross section as this is more comfortable. D+ cup bras tend to use a sturdier wire construction with a deeper, flatter cross-section for added strength and rigidity. Some full bust brands also prefer a U shaped wire generally, as larger busts tend to be rounder.

Less Common Wires
Some other types of wire you may see are:

shallow demi wire_1
Shallow demi wire – used in triangle cup bras, which are a cross between a soft and an underwired bra.


Mono underwire (aka Domino wire) – can be fully rigid or have a flexible silicone joint. These are to provide a look rather than practical benefit – they are difficult to pattern cut for!

Titanium memorywire

Titanium memorywire – this tends to have a round cross section and has the advantage of being able to move in all directions with the body. They also can be squished up and ping back into shape (see above) which is pretty cool!

Strapless Wonderbra

Wonderbra via ASOS

Wonderbra plastic ‘hand tech’ support – created by and unique to Wonderbra, they developed a plastic support that looks a little like splayed hands which with a wide elastic underband works like an underwire, hidden inside the bra.


Overwires and separators – these are used to create a certain look and do not really have a technical function, though their use can affect bra fit. Overwires go above the bust, separators (see below) go in between them as a design feature.

3D wires – one flaw in most modern wires is that they are two-dimensional – curved in one direction only, which is why I can lie them flat to photograph. But as you may have noticed, your body has both the curve under your breast and the curve of your ribcage! Some research is being done to create a 3D underwire as, in theory, it should be more comfortable to wear (though the curved shaping idea was in use in both 1950s overwires and vintage French mono underwires).

Wire-related Tips for Choosing a Bra:

  • No bra is better than any other overall. Each has its own function, and what works for you might not work for everyone.
  • Different wire shapes help produce different bust shapes. So what shape would you like?
  • Underwires shouldn't be uncomfortable, but you can get discomfort from pressure points with larger cup sizes. Shop around for the best bra shape for you, but also be willing to try a non-wired bra.
  • The more the wire aims to change your shape, the more likely it is to cause twinges. Push up bras with plunge wires are pretty harsh, so perhaps leave them for short term wear if you're having problems.
  • As a general rule, to be comfortable the wire must not sit on any breast tissue. If it does, the wire may be too small or not pulled out enough by the fabric of the bra wing. If this is the case, then do not buy the bra!
  • This also means that if you have a big difference between the left and right breast, fit to the largest breast.
  • Making your own bras? Ignore hopeless descriptions such as ‘short, super-long and extra-long wires’ which are far from helpful and use this article as a reference!

Do you have any more questions about underwires? Please leave them in the comments, and I'll try to answer!


Article Tags :
Cora Harrington

Founder and Editor in Chief of The Lingerie Addict. Author of In Intimate Detail: How to Choose, Wear, and Love Lingerie. I believe lingerie is fashion too, and that everyone who wants it deserves gorgeous lingerie.

34 Comments on this post

  1. Mona Zhang says:

    I’m curious why the Day Bra wire is called “J”. To me, a plunge looks the most like a “J”! Am I missing something here?

  2. Adiva says:

    This article was so beneficial to me because I am sick of the bras I have and I’d rather create my own. The article helped me to gain a better understanding of the types of bras and whats for support of fashion.

  3. Mercedes says:

    Hello! Thank you for your knowledge. Every woman needs this. My question is this. I just purchased a bra from Fauve by Fantasie. I am now a 36E. I noticed the underwire is too short on the outside channel. It’s about an inch from the upper edge of the band on both sides. This doesn’t seem right for such a well known and well made brand. I would like your opinion.
    Thank you.

    • Julie says:

      The space left is called ‘wire play’.
      When you move around in a bra there is a fair bit of tension, so it’s usual to leave space for the wire to move with you. When there isn’t enough space for the wire to move your wire cuts through and that’s why your underwires sometimes come out.
      I hope this helps.

  4. Virginia says:

    This is a fantastic resource. Thank you! I will definitely be sharing this with all the ladies in my life :)

  5. Erin says:

    Hi I enjoyed reading this article. I am wondering which style of bra you would best recommend if I often experience uncomfortable underwires. Would you better recommend buying a push up or Demi bra ?

    • Debbie says:

      Hi, You can go to, input your measurements, select which torso or torsos have the most similar shape to yours and it will select those bra types with and without underwires to help. The self measurement includes your taking the actual measurement of the largest of your breasts so that their program gives the best bras for you that will give the best fit! PS:It includes conversion from metric to standard.

  6. Marcel Ellis says:


    Thank you a great article. Question: Do you know where I can buy the overwires. separators. Wife has had breast cancer so some of the dresses I make for her need some extra support in this area. Australian contact would be great as we live in Adelaide.


  7. Valerie Lynn says:

    I just bought three brand new VS bras, that are super duper cute. Only problem is the underwire! Because I have such big blessings (42DD), it’s hard to find bras without the underwire and still feel sexy. I’m debating taking them back to try and find something else that’d be more comfortable, and just cutting the wires out because I have before. But if I cut them out, do you think it’d be easy to sew back up?

    • Debbie says:

      Hi, I’m an FF to G cup and have removed underwires before. What you do is get a small pair of seamstress thread cutting scissors or even scissors used to cut hangnails and snip about a 1/4 inch slit on either side of the bra where the underwire channels are and then work them out. You will need to hook your bras tighter and they will feel softer but with less support!
      Also, if you are sized correctly, the underwires should never jab into the sides of breast tissue but gently outline the outer portions while providing the lift and shaping per the bra design. Please self measure per the instructions at so you can have an easier time finding better fitting bras. I was shocked by what my true size was because for years I was buying 38 C and D bras (American sizing) but I’m a 30 FF to 30 G using UK which translates to 34 DDD to 36 DD American because in US the band measurement is taken from under arms and around upper chest and in UK the measure is around the rib cage under the breasts because the band is where the greatest percentage of support comes from!

  8. Julia doemer says:

    Would you be able to advise on where to buy a 80C plastic underwire?
    I am not wanting to walk around being an antenna, and wear metal of any kind on my body ,if I may put it that way.
    Are the ‘wires’ available in a strong plastic? Or do they only come in metal?
    Thank you for your help and interesting article

  9. Granny says:

    Wires are U shaped but the base of my bust is a straight line.

  10. Jeannette says:

    Where can i purchase those separators from. 5″Depth 4″wide?

  11. Rebekka says:

    Hi! Thank you so much for this information. I am trying to find information about making an over wire bra… and also making an overwire bullet bra. Do you have any suggestions? Can you just use underwire and separators? Thank you! R

  12. yukki says:

    such a great guide! Do you know what is the difference between bra wired on and off cradle?hope to hear from you as soon as possible,thanks!

    • Wire on or off the cradle is referring to whether or not the wirecasing is applied to the cradle or the cup. Where it is wired onto the cup (and there is no cradle only a CF bridge).

  13. dg says:

    Thanks for the informative post. I’ve been trying to figure out how to categorize my breasts for a while and see a resemblance in the photo of taking a root trace using a flexicurve. Would you mind telling me how you would classify the root width, breast shape, and level of fullness in that photo? My root seems to start right at the edge of my ribcage and I believe my breasts are FOB with 1-2 fingers’ width spacing between them. They are a little softer and end a little lower on my body (after breastfeeding) than in that photo but have similar fullness. I mostly wear 70E/F Ewa Michalak CHPs (the CHs, though unfortunately no longer available, fit me better) for the shape, projection and padding; the underwires may be a little narrow but not painfully so, and I tend to spill towards/over the center of the cups as the day progresses (which happened less in the CHs as they were cut straight across the top). In the Freya Deco (30F), which I like for being molded, I get orange-in-a-glass and gapping where the cup meets the strap (making the cup edge more visible under clothing), but a nice, rounded shape. I never achieve more than Marie Antoinette cleavage, but I’m fine with that. If you have any suggestions for other bras I could try, I’d love to hear them. Thanks for your help!

    • Melissa says:

      Hi dg! I’m Mel, Bra Specialist fitter, and it sounds like there are a few things going on with you. When was the last time you got fitted? There might be a chance that you are wearing the wrong size. If you are spilling over the top there are a few things you can look at: a bigger cup size, longer straps, a cup with more depth or a cup with more hight (coverage). If your wires are giving you pain, specially in the middle of the cup and on your rib cage, the size of your back/band is too big and riding up. Also with this check that the bra is sitting low enough on your back. You should have the bottom of the band sitting parallel to the floor, as close to your waist as possible and underneath your shoulder blades. If once you adjust it still moves up, it is definatly too big. A great brand you could try is called Evollove, look for it online. Brava is great for difficult sizes too.
      Hopes this helps you out a bit.

  14. Sue says:

    Do you have any thoughts about wires in bras fir women following breast cancer surgery? Ive been wearing non-wired for 2 years, just back into wired, but not getting on too well at all. Thoughts most welcome. Sue

  15. AlexaFaie says:

    I love this!
    I wish more places would use the plunge wire in their bras for every day wear. I find it impossible to wear balcony/balconette bras as the wire is always too high up in the center front so digs into my breast tissue there. Too many large cup brands seem to think that one needs that kind of wire and neglect to make bras using a plunge wire. I’ve come to be able to tell the difference now. No, that large bust bra you claim to be a plunge is not a plunge, its using a “regular” underwire. It won’t fit me no matter how much I will it! ;) And that’s before I even get to talking about them thinking that large bust = widely-spread-living-under-the-armpits-breasts! Some of us have narrow breast roots and a ton of forward projection and so larger cups often have the volume distributed incorrectly for us.
    Took me so long to find a brand which has the cups close enough together, with a low enough wire at the front and enough forward projection and sadly they seem to not be producing more bras in that style. All the current renditions are on clearance and all the new offerings for their large cup bras are balcony bras or full cups. There are no new plunges not even in colours I don’t like!

  16. Lyzzy Beswick says:

    Correction – should read ‘it is not simply a case of altering the pitch of the wire’. The shape of the different styles of wire’s curve is different also.

  17. Hi Chelsea – Apologies for the late reply I had missed seeing your query till today. Cora is correct in what she says – plus fit sizes have underwires with stronger metal etc. To answer you point specifically though – All bra wires cross grade – so yes a 34B bra wire is also a 32A and a 36C – they are interchangeable, and generally you buy them as a wire for all those sizes (it being one and the same) and not per one specific size. In terms of taking one type of bra wire and using it as another you can’t do that because for example a plunge wire is so much shallower than a day bra wire that you could never find the correct curve to match off from one to the other. It is not simply a case of the pitch of the wire. I strongly recommend you buy the correct bra wire designed and developed for the style of bra you are wanting to make.

  18. Hi Chelsea – Apologies for the late reply I had missed seeing your query till today. Cora is correct in what she says – plus fit sizes have underwires with stronger metal etc. To answer you point specifically though – All bra wires cross grade – so yes a 34B bra wire is also a 32A and a 36C – they are interchangeable, and generally you buy them as a wire for all those sizes (it being one and the same) and not per one specific size. In terms of taking one type of bra wire and using it as another you can’t do that because for example a plunge wire is so much shallower than a day bra wire that you could never find the correct curve to match off from one to the other. It is not simply a case of the pitch of the wire. I strongly recommend you buy the correct bra wire designed and developed for the style of brayou are wanting to make.

  19. chelsea says:

    Many underwires are marketed as different sizes. Is the size difference necessary? If you order a day bra underwire, can you just alter it to fit the wearer? A 32A underwire could be used for a 36C? It would just depend on the placing on the band, right?

    • Cora says:

      Hmmmm…Lyzzy could answer this much better than me, but not exactly no.

      For example, the underwires used in DD+ bras are often a different shape than those used in A-C cup bras. They tend to be sturdier and narrower and rely upon the weight of the breast to open them up. You could use them in a sister size, but the wire shape will probably feel very “aggressive” and “tight” to someone who’s used to wearing a C with a non-full bust wire. And I’m speaking from personal experience here. I prefer to wear a 34C, and I’ve tried some bras from full bust brands in a 32D. It’s “technically” my size, but it’s super-uncomfortable because the wire is all wrong for my bust.

      Regarding the example you gave, the wires in a 32A and a 36C are for different bust volumes, so they wouldn’t be the equivalent shape/size. If you wanted to use a 36C wire in an A cup bra, that A cup would need to hold same cup volume, so you’d need to try it in a 40A, the sister size to 36C.

  20. Lyzzy Beswick says:

    Glad to have been of help Lana. Hi Xelestial – well basically you have a greater weight to distribute with larger busts and so naturally certain points will be pressure points when wearing a bra. the better the engineering of the bra the less pressure points and pressure. As a general rule larger cup size bras should be tighter in the underband than core sized bras, and when this is done correctly it should stop the bra slipping down. It is a while since I wrote this – but in terms of suggesting wireless for large cup sizes I think I had a specific person’s bras in mind. There’s a lady who does a very good wireless bra used by professional sportswomen and they are each made bespoke with the aim of stopping back pain etc from large breasts. If you bear with me I shall try and look out the details of this from my archive for you. I haven’t come across women choosing to bend their underwires and I wouldn’t really recommend it. As yet no one is commercially producing a 3D wire, it is just that research has been done into it and in principle it seems to be an idea with potential. That is a big question to answer – but it would vary in that it wouldn’t be a permanent or regular bend if done by hand, the curvature would not simply be a kink type bend in one place which is what you are likely to get if bending your underwire yourself and also I think that material used for the 3D underwire would be key to it’s potential usefulness and effectivieness – I expect that it would work well in a memory wire/metal, and would require different springing qualities to that of a standard wire.

  21. Xelestial says:

    I am curious about the statement that underwires can cause pressure points with large busts. I am above a K cup and I am currently trying to figure out why underwires tend to slip down and dig in the ribs for those with small backs and large busts. I have heard it is due to a number of factors, but is basically due to bra manufacturer ls not understanding the unique needs of full bust women and creating bras that have unstable tension to support the large breasts on a smaller frame. Yet I feel this can be remedied as I experience the issue to varying degrees in different bras. But instead you suggest that we should be willing to try a wireless which is known to lack proper support. Do you not believe that the issue of pressure can be solved or do you just not have knowledge in that particular area at this time?

    Also how are 3D wires any different from women simply bending underwires to the contour of their bodies? I appreciate any insight you can give me and loved the article. I would love to know more about bra construction to help myself and others, thanks.

  22. Lana says:

    THANK YOU! This article is extremely helpful & I found it at the perfect time. I could kiss you!

  23. Hi Ladies, Glad you enjoyed the article. Thursday – yes so will I be it’s something that has been in development on a small scale for many years not sure when or if the 3D wire will be released commercially – the technology and concept behind it is sound though. C.C. – Well it depends on the quantity you are wanting to buy wires in? Really wholesalers are only going to supply by the 100-1’000’s per size I’m afraid. Buying in single pairs – the Bra Maker’s Supply has wires more reasonably priced than most in the UK: Warmest Regards, Lyzzy

  24. C.C says:

    I really enjoyed your article. I am interested in making bras and I have been having a hard time to find underwires to purchase wholesale. Would you know where I could go to find underwires to be bought in wholesale in the UK?

    Kind regards,

  25. Thanks so much for this. I hadn’t realised just how much they contribute to the support of the breasts. I’d also been wondering what the assistant in the Triumph store was going on about when she told me that they have 3D wires in their new full cup range, Beauty-Full. Makes much more sense now!

  26. Thursday says:

    I also found this an interesting read – thanks Lyzzy! I’m curious to see how innovations in 3D wires might improve the fit and comfort of bras.

  27. Molly says:

    Loved this article! I’d love to read more about bra construction and the science/physics behind it.

  28. Laura Brasinha says:

    This is so super mega interesting! I love this article. I’m sharing this with everyone!

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