Tatami Mat (Twin 79″ x 39″ x 0.5″), Japanese Traditional Tatami Mattress, Natural Rush Grass Floor Tatami Futon Mattress for Sleeping, Sitting, Yoga, Relaxing (Twin). This tatami mattress works perfectly as a base for a traditional shiki futon (shikibuton), so you can use it sleep on the floor to straighten your back.