The heart of the Natural Rubber Crib Mattress is the 5 inch core of Firm Natural Rubber that provides the perfect feel for a newborn baby. Surrounded with quilted layers of pure wool and encased in an organic cotton fabric, the Natural Rubber Crib Mattress is extremely durable and resilient. Click HERE to read more about the natural rubber, cotton, and wool used in this mattress and to view the organic certifications. The natural wool acts as a natural flame retardant. This mattress meets all the higher CA flame retardancy guidelines. Absolutely NO chemical flame retardants added. Fits all standard cribs 28" x 52". Approximately 5" thick.