Band and cup

A band is a closed elastic loop under tension. Tension times contact area gives pressure, and pressure is what keeps the loop from sliding upwards when weight is hung on the front of it. A wider band spreads the same tension over more skin, which is why wide bands are more comfortable at larger cup volumes rather than less.

Anchoring matters as much as tension. The band needs to sit low and level, following the line of the ribcage rather than sloping up at the back. Once the back of the band climbs above the front, the loop is no longer horizontal and every bit of downward force pulls it further up.

Why the loosest hook first

Elastic loses recovery with use. Every wash cycle, every stretch and every hour at body temperature takes a small amount of it back. Two or three rows of hooks exist so that a band can be tightened progressively as it ages. Starting on the tightest hook means the garment has no remaining life once the elastic relaxes, which usually happens well before the fabric wears out.

An underwire is not a support device on its own. It is a perimeter: it defines the edge of the cup and holds that edge in a fixed shape against the chest wall so the cup can be shallower and lighter than it would otherwise need to be. A wire is doing its job when it sits in the crease where the breast tissue meets the ribcage, all the way round, touching the body but not pressing into tissue.

• Wire width should match the root of the breast, which is the width of the base where it joins the chest.
• Wire on tissue at the side is the most common wire fault and produces real soreness within hours.
• A wire that sits forward of the ribcage at the centre means the cups are too small or too shallow, not that the wire is faulty.
• Wire width scales with band size in most ranges, which is why sister sizing changes more than volume.

Volume is only one of three variables. The other two are depth and width, and they are what make two garments in the same printed size fit completely differently.

Depth

How far the cup projects from the chest wall. Projected, full on bottom tissue needs depth. A shallow cup on projected tissue cuts across the front; a deep cup on shallow tissue wrinkles at the top.

Width

How much of the chest the cup spans. Determined largely by the wire. Too narrow puts the wire on tissue; too wide puts it under the arm.

Seaming

A moulded cup is one continuous shape with no seams and no adjustability. A two or three part cut and sewn cup places seams deliberately to direct tissue, usually upward and inward, and is far more adjustable in shape at larger volumes.

Volume tells you which size to pick up. Depth and width tell you whether that size will actually work on this body.

Straps stop the top edge of the cup from tipping forward and hold the shape of a moulded cup against the body. They are a stabiliser, not a suspension system. Set them so that a finger can be lifted about two centimetres away from the shoulder with mild resistance. If they need to be tighter than that to keep the bust in place, the band is the component at fault.

Strap position varies by style: wide set straps on a balconette are inherent to the shape and will slip on sloping shoulders no matter how well the band fits. That is a compatibility problem, not a sizing one.

1. Band first, always. Firm on the loosest hook, level front to back.
2. Scoop the tissue forward into the cup and settle the wire behind it.
3. Judge the cup on the top edge, the side and the centre panel.
4. Set the straps last, and set them loose.

Anything still uncomfortable after that sequence is a shape problem rather than a size problem, and the answer is a different cut rather than a different number. The styles section sets out what each shape is built to do.