A strapless bra without underwire relies entirely on band compression and silicone grip to stay in position. At D cup and above, breast weight is significant enough that a fabric band alone, without a wire supporting from below, will ride down under load. An underwire in a strapless bra provides the structural foundation the cup construction anchors to.
What to look for
The key elements: a wire long enough to span the full base of the breast; a cup tall enough to fully contain the bust; a firm band that carries the support load; and silicone grip that grips skin. Try it on the loosest hook with the straps off: the band should feel genuinely firm, and if it doesn't, go down a band size and up a cup. Browse by cup size: E cup, F cup, G cup. For convertible options, see multiway bras.
Or browse all strapless bras for large busts.