It depends on what the mattress is made of.  Substances such as wool and cotton are not as flammable as synthetic materials. In organic latex mattresses, wool is typically quilted into the cover. Wool is a natural flame retardant. Wool has many other benefits as well. It helps to regulate temperature, which means you can sleep cooler and drier. It is renewable, breathable, and naturally dust-mite resistant, as well as providing a soft layer for the comfort of your mattress. Organic cotton tends to smolder, not burst into flames.