HANGABLE CLASSIC SKEEWBACKERSTM - 1/4"
Hangable Skeewbacker Classic 1/4 in. mosaic backers are designed to have a hanging system installed directly to the backer. One is available at a discount when you buy the backer, or you can make your own. There are 9 sizes to choose from and you choose to make the rectangles portrait or landscape with hanging system placement. They are constructed from a rigid polystyrene foam core sandwiched between waterproof membranes.
see this short video on installing the hanging kit