An underwire is an arc ( a semi-circle) of (usually) rigid material which is usually made from either resin, metal or plastic.

Plastic has a tendency to break snd is usually used in cheap mass produced lingerie, or in swimwear so the wire doesn’t rust. Generally the underwire are carbonised steel that has an outer coating of nylon with a extra coating at the ends, so the wire doesn’t come through the wire casing. The wire also has a coloured tip to indicate the size of the wire.

Although the wire is usually an arc shape, there is a mono wire which is one continuous wire which looks like a soft ‘w’ shape, they are used mainly for an aesthetic design purpose rather than a practical benefit, also the pattern for these wires can be a nightmare to cut.

The wire was patented in 1931, a ‘U"‘ shape to be worn flat against the chest wall, but the underwire didn’t really take off until the 50s and was just used as a fashionable silhouette.

How the underwire works

Nowadays the bra wire is designed to act as a cantilever(like a wire bridge) and lift the breast up and in. Let me explain, the correct wire for you would be one narrower than the natural root of your breast, then once inserted into the wire casing and worn, it springs out towards your arm pit and the tension holds and supports your breast. So the weight of your breast is transferred into the cups, along the wire and down into your band. This is why it is stated that you shouldn’t be looking for much support from your bra straps, as a correctly fitted bra should be supporting your breasts from the underband (and wire ).

DIFFERENT SHAPE WIRES

Balconette

The wire is a ‘J’ shape, it’s also used in full cup bras. It’s shorter in length and it has the greatest difference in height compared to the other types of wire, these wires are the most similar shape to the natural shape of the breast-root.

Plunge/Push-up

These wires are put into the bra at a sharp tilt (the angle of the cup is different to start with than the balconette), so the breasts are pushed together and upwards. The wires are banana shaped and can be known as a ‘rocker’ wire, with some being more hooked at the centre front. The bras themselves don’t provide as much coverage as the balconette .

Strapless

These wires are a deep ‘U’ shape. The wires are the same height at the centre front and at the side. The breast is designed to fall completely into the wire shape so it is fully contained and supported and projected forward.

Over D cups

The wires used are more rigid and sturdier, but be careful on getting wires too sturdy as this may lead to bruising of the breast as it can’t flex that much.

To learn more about Bra components please see below:

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Disclaimer: After writing this blog I realised that I didn’t have all wires to show you the shapes so instead of taking off wires off the internet from someone else’s work I decided to draw them. It’s only when putting the image in that i realise they look like double ended dicks! But it made me laugh so much that I decided to keep it in. If you want to see better shapes of the wires please google the shapes!!

Different types of underwires for a bra