I have a pergunta about movie costumes

I hear some actors and atrizes say they get to keep their costumes if they request it in their contract? Does anyone know if that is true, I am not very good at looking things up on that level. I do know that as far as show case costumes, if it is true the ones in the show case are usually the double that is made or the actor or actress owns it but its on display. Anyone know anything.??? I would amor to keep all the costumes that I wore I was an actress.