http://catalog.usmint.gov/webapp/wcs/stores/servlet/ProductDisplay?catalogId=10001&storeId=10001&productId=13900&langId=-1&parent_category_rn=10211

The coins are not made of silver. They are made of the same medal as the coins in circulation. They are struck more times than circulated coins.

The Presidential spouse coins are made of gold but the presidential dollars are not.

Also note "Distinguishing this collection are the dime, half-dollar and five commemorative state quarters, all of which are produced in lustrous 90% silver." Presidential dollars are not mentioned in the silver category.