HOUSTON, Aug 01, 2013 (BUSINESS WIRE) --Mattress Firm, Inc., the nation's largest specialty mattress retailer today announced their partnership with Imagination Foundation as the Challenge America sponsor of The 2013 Global Cardboard Challenge. The Cardboard Challenge is a worldwide celebration of creativity during the month of September, where children are challenged to design and create using cardboard and recycled materials. The Challenge culminates around the world on October 5, 2013, on the global Day of Play.