We take a firm 4.5" natural rubber core and cover it with our organic wool moisture pad fabric. This makes a mattress that has no cotton on top at all to get bacteria or urine on. It protects itself. It is the best for anyone that has a severe dust mite allergy or a mold problem in their home. The wool and the rubber protects from insects and from molds. Recommend a organic cotton quilted pad to protect from wetting or spills.