The sleeping surface of a folding sofa bed usually consists of a mattress that is integrated into the design. The mattress can vary in thickness and comfort levels, ranging from thin and firm to thicker and more plush options. Common mattress materials include foam, innerspring, or a combination of both.

Folding sofa beds are available in a variety of upholstery options, similar to regular sofas. Popular choices include fabric, leather, or faux leather upholstery. The upholstery material can affect the overall look, comfort, and durability of the sofa bed. It's important to consider factors such as personal preference, maintenance requirements, and the intended use of the sofa bed.