We designed the California King 5 Inch Wool Shiki Futon Mattress for anyone seeking a supremely comfortable but firm mattress filled with USDA Certified Organic Cotton. Our Traditional 5 Inch Wool and Cotton Shiki Futon California King Size Mattresss are firm when used with a traditional tatami mat. no matter what size you choose each mattress is designed to last a lifetime when taking proper care.Cotton is a natural, renewable, biodegradable and sustainable fiber. Cotton breathes, so it stays cool, is never itchy, and it's an outstanding insulator to provide warmth in the summer & heat in the winter.