Old Navy and Terracycle have partnered up to create the Flip Flop Brigade where every time you send your old used flip-flops into TerraCycle, you can get new flip flops and at the same time help out Mother Nature by diverting waste from landfills.   For every shipment of about 25 pairs of flip-flops (or 50 individual flip-flops), Old Navy will provide you with a coupon for a FREE pair of Old Navy flip-flops plus 25 additional coupons, each worth $10 off your purchase of $40 or more. There are no signup or participation fees, and the shipping is covered by the program.