You need to read this entire website to understand why the Nook mattress is the most considered infant mattress and sleep system. The pebble mattress is constructed of several layers of materials... all non-toxic. The interior of the mattress is made from 100% natural latex, PETE and organic wool. The exterior pebbled surface allows for increased air circulation and the natural eucalyptus fibers interwoven with zinc absorb moisture to keep baby asleep. Okay, it's $550 but maybe you can opt for a crib sheet or pebble blanket instead.