They're easy to use and 100 percent re-usable. Made of polypropylene, each flower has a magnet embedded in it for attaching directly to metal. Or you can easily attach them to any wall using the tacks that are also included. The flowers range from 2.5" to 4.5" in diameter, which lends them nicely to any number of scattered arrangements.
$40 for a set of 25 at Urban Outfitters