5 thick Open-celled polyurethane core, durable and conforms to the shape of your body for firm support. * Summer Side with Cotton ticking for natural Body Cooling. * Winter Side with Wool ticking for additional warmth in winter. * FlameWatch technology - California TB 603 lab tests designed to prevent an intense mattress fire for 30 minutes. * Resilient, high density polyurethane foam will not lose its shape.