I've read that if you bend the silicone and see white streaks, it's got other substances and should be avoided. Although I have cupcake kits with silicone bakeware, I still try to avoid using them as much as possible.
We have some and they seem like they hold onto the soap used to wash them. Like when we bake we swear we can taste soap on the muffins? Now I just use them for dipping sauces to quickly and easily contain dipping sauces or sides on our plates.