What is a shikibuton, and how is this one constructed?

A shikibuton is a traditional Japanese-style folding floor mattress designed for use directly on the floor or on a tatami mat. This 3.5-inch version features 2.5 inches of 1.10 high-density 38 ILD soy foam topped with 1-inch all-natural Dunlop latex, giving it a medium-firm feel with a softer top surface. It's hand-sewn in The Futon Shop's California warehouse with a removable, washable organic cotton cover.