Method of making foam mattress

A process of forming substantially simultaneously a convolute pattern within opposing outer surfaces of at least two bodies of a plastic foam material comprising locating pairs of said bodies in a surface-to-surface juxtaposed position so that said outer surfaces reside substantially in a common plane, cutting said convolute pattern in each of the juxtaposed surfaces of said bodies as said bodies and a cutting instrumentality are moved in relative motion and said cut moves from one body across said common plane to the other body, separating the bodies after said convolute pattern is cut, and allowing a portion of each protuberance of each body extending beyond said outer surface to break away whereby said convolute pattern in the form of a plurality of flats and cavities resides completely within each body.