We start with a natural organic Rubber Core. Choose from 4″, 5″ or 6″. We cover the rubber core with either our Waterproof Jersey material made of tightly woven organic cotton OR our Cotton Quilted material which consists of a layer of wool sewn between two sheets of GOTS organic cotton fabric… our double knit on top and a heavy muslin on bottom. We highly recommend a wool felt puddle pad for the Cotton Quilted mattress to protect it from moisture. Both coverings can be easily removed from the rubber core for laundering.