These are mattresses we designed specifically for young children. We take a 4.5" natural rubber core and cover it with our organic wool puddle pad fabric. This makes a mattress that has no cotton on top at all to get bacteria or urine. It fully 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. Made for kids up to 100 lbs or so. When child gets heavier you can add a 2" topper. This is custom Crib Plus - so up to 55.5" x 38 x 4.5"