Mattresses and methods for processing a flexible foam material for use in a mattress to provide a mattress foam material that has more consistent firmness over time and area. The methods include pre-conditioning the foam pad or mattress by applying a force across a substantial portion of a major surface of the mattress to compress or stretch the height of the foam, the length of the foam, and/or the width of the foam to break or open closed cells. In certain embodiments, the force is applied by repeatedly pressing a platen against the foam pad or placing the foam pad between one or more rollers.