Strapless

• A wider band, often three to five centimetres deep, sometimes with a bonded or moulded lower edge to spread pressure.
• Firmer band elastic with less give, since there is no strap to compensate for slippage.
• Silicone strips along the top edge of the band, and sometimes the top of the cup, to add friction against skin.
• Longer, stiffer wires that extend further under the arm to anchor the cup laterally.
• Cups built with internal structure, either moulded foam or firmly seamed panels, so the cup holds its own shape rather than relying on strap tension.
• More hooks, three or four columns rather than two, because the band must be adjustable over a narrower comfortable range.

The measured size is still the starting point. The common advice to buy a band size down in strapless is right often enough to be worth testing and wrong often enough to be worth testing carefully. The reason it sometimes works is that the extra friction and firmer elastic of a strapless band can tolerate a tighter fit than an everyday band. The reason it sometimes fails is that a band too tight to breathe in comfortably will be abandoned by mid evening.

If a band size is dropped, add a cup letter to keep the volume: 34D becomes 32DD. That is standard sister sizing, and skipping the cup adjustment is why some people conclude that strapless simply does not work for them.

A strapless bra that has to be hoisted twice in an evening is not a strapless bra that fits. It is a normal bra with the straps removed.

1. Fasten it, then raise both arms straight above the head and hold for ten seconds. The band should not move. This is the whole test in one gesture.
2. Bend forward from the waist. Nothing should fall out of the top of the cup.
3. Sit down and lean back. The top edge of the cup should stay in contact with the chest.
4. Walk. If the band creeps down after twenty paces, it is too loose or the silicone has lost its grip.
5. Wait an hour. Body heat and skin moisture reduce silicone friction, and the real behaviour of a strapless bra only shows up after it has warmed up.

Silicone grips by friction against dry skin. Body lotion, oil and sun cream all defeat it, so anything applied to the ribcage before dressing should be given time to absorb fully or skipped in the band area entirely. Heat and perspiration do the same thing more gradually over an evening, which is the reason strapless behaves so much better in a cool room.

Silicone also collects skin oils and dead skin, and once loaded it stops gripping permanently. Wiping the strip with a damp cloth after each wear and letting it dry fully restores most of that. Detergent residue does the opposite: it leaves a film. See hand washing for the rinsing routine that avoids it.

Strapless is a compromise by construction, and the compromise gets steeper as cup volume increases. At larger volumes a long line strapless, which extends down towards the waist and borrows anchorage from the ribcage over a much larger area, does the job far better than a conventional one. Adhesive cups without a band are a different proposition again: they attach to breast tissue rather than the ribcage, provide coverage rather than support, and are best treated as a solution for a specific neckline rather than for a long day.

Convertible bras with removable straps are worth naming as their own category. A conventional bra sold with detachable straps is usually built as a strapped bra and will behave like one with the straps off. A genuine strapless with optional straps is built the other way round. The tell is the width and firmness of the band.

For which necklines need what, see special occasion.