A mattress is a fabric case filled with material, used for sleeping on. Mattresses contain spring coils and foam. The foam is used on the top of the mattress for your initial feel when you get into bed. The coils are what support you throughout the night as you sleep. Coil count, Innerspring Coil Systems VS Pocketed Spring Coil Systems and how thick of a mattress it is that you need, are all factors to take into account when buying a mattress. Free Delivery!