Wood and metal are the most popular futon frame materials. If you go with the former, hardwood lasts longer. As for the mattress stuffing, cotton and foam weigh less and hold their shape well. A cotton-polyester blend is even lighter and you’ll still be able to avoid sagging. A cotton-wool combo is ridiculously soft—but not very flexible. Innerspring mattresses have a spring between layers of foam and cotton, and although they weigh more, they’re flexible and feel similar to a traditional mattress. Just don’t forget a futon cover to protect your investment.