Fake silk ones.

hee hee... reminds me of when I was watching the show on PBS "Mystery" when they were doing the Cadfael series. One of the episodes is called "the Rose Rent", which is quite a good one. Oh but the horror of it when I realized that the rose bush was a VERY fake one... plastic and fabric all. Sigh. Once spotted it is hard to ignore, and plastic never looks good in a medieval context.

Forgive my ignorance, since I am more an antique rose person than a HT person, but isn't the rose in American Beauty supposed to be the rose "American Beauty"?

No, the real American Beauty is a deep pink hybrid perpetual. The roses in the film were deep red hybrid teas, but I also think they were probably silk. Here is a photo of Annette Bening with the roses. I think it looks a little like Ingrid Bergman but I think they are fake. The roses used in the petal scenes, and the single stem in the promo shots, are probably all some florist variety (if they aren't also silk).