These are nice to have handy, if you have a social occasion to be strapless or just wearing a tank or spring dress. They are sticky, that's what holds them in place. After wearing I washed mine with a little Woolite and let air dry before returning to storage. If you take care of them they should last.
I am NOT a large busted woman (b cup) so they work great. I can't say how they would work for large cups because there's no support, they just cover the nipples so they don't show. Perfect for A and B cups.