Bra Underwires – Nylon-Coated and Galvanized Options

Support Wires for Bras, Corsets and Swimwear

Bra underwires are curved wire inserts sewn into a dedicated channel at the base of a cup. Their role is to support the cup architecture and help the garment retain its designed shape around the underbust area.

They are suitable for underwired bras, bikinis, swimwear, corsets, bustiers and custom garments with structured cups. The quality of the final fit depends on matching the wire to the actual cup pattern rather than selecting it from the printed size value only.

Available Underwire Constructions

• Nylon-coated underwires: Metal-core wires covered with a smooth plastic external layer.
• Galvanized underwires: Wires made from galvanized metal construction.
• Sizes 75–110: A size series intended for different cup dimensions and underwire contours.

Material Choice: Nylon-Coated or Galvanized?

A nylon-coated underwire has a metal core and a plastic outer layer. This outer finish can be useful where the wire will sit inside a lined cup or fabric channel, as it provides a smoother contact surface around the wire.

A galvanized underwire uses galvanized metal wire construction. The best material is determined by the cup build, the type of lining, the underwire-channel fabric and how the garment is designed to be worn. Both options should be tested in the completed sample garment before production is scaled.

Underwire Size Selection

Size 75, 80, 85, 90, 95, 100, 105 and 110 identify the available product series. They do not automatically define a cup letter, international bra size or universal cup shape. Different patterns can use different wire widths and depths within a similar size family.

Reference Dimensions for Size 75

The size 75 nylon-coated underwire has a 17.2 cm / 6.77 in wire contour, 10.4 cm / 4.09 in inner width and 5.2 cm / 2.05 in depth. These values apply to the size 75 reference only. Larger sizes have different contour, width and depth values.

Pack Quantity and Production Planning

Underwires are supplied in packs of 50 pieces, equal to 25 matching pairs. This pack structure is practical for bra and swimwear production because each completed garment generally requires a left and right wire.

Before bulk production, test the selected wire inside the real cup channel and finished lining. A wire can appear correct when placed on a paper pattern but sit differently once fabric thickness, seam allowance and channel construction are added.

Common Mistakes to Avoid

• Choosing a wire based only on the size number
• Skipping the cup-pattern contour comparison
• Ignoring depth and inner-width measurements
• Using a channel that is too tight or too loose for the wire
• Leaving the wire ends without adequate protection inside the garment
• Assuming that 50 pieces means 50 complete sets rather than 25 pairs

Frequently Asked Questions

What is a bra underwire used for?

It supports the lower structure of the cup and helps the garment maintain its intended shape around the underbust line.

What is the advantage of a nylon-coated underwire?

It combines a metal support core with a smooth plastic outer layer for use inside a fabric underwire channel.

Are galvanized and nylon-coated underwires interchangeable?

Not automatically. The right option depends on the cup construction, lining, channel material and intended garment use.

Does a size 90 underwire always fit a 90-size bra?

No. The wire must also match the cup contour, width, depth and channel construction of the specific bra pattern.

How many pairs are included in a pack?

A 50-piece pack contains 25 matching pairs of underwires.

Can these underwires be used in bikini and swimwear tops?

Yes. They can be used in structured bikini and swimwear cups when the garment has a suitable underwire channel and the wire is matched to the pattern.