It may be a question of semantics, but they tend to be firmer, but they are not by any means hard.
As a matter of fact, their capsular contracture rate is up to 75% lower than standard gel, so in a sense they are less likely "to get hard."
The firmness, however, is where they get their advantages. If you want an implant to maintain a shape, to be less likely to ripple, to be less likely to break, for the gel to be less prone to migrate if it does break, then the device needs to feel a bit firmer.
The firmness issue is only a problem in women with loose and somewhat floppy breasts. It is never an issue in a firmer, younger breast.
So for a thin, young, small breasted woman who has not had a baby, they feel very much like her own tissue. But they are firmer in someone with looser and more mobile or pendulous breasts. The latter group of women is a group that I warn about the firmness, but it is not an issue for younger and tighter-breasted women.
