If you're refering to products like Bare Escentuals Bare Minerals, or other "mineral" based foundations, they really aren't powders per se but finely ground minerals. Believe me, they do have great staying power. Just drop some on your clothing or your carpet and you'll find out!! Regular powder just doesn't have anywhere near the staying power that the mineral foundations do. Powder is meant to "set" your foundation, not act as foundation. Mineral foundations even out your color and cover any problems you have making them great coverage foundations. I also use my mineral concealer (BE Bisque) on breakouts to help get rid of them as well as cover them. I know the BE foundation also has a SPF of 15.
Hope this helps!
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