Our Ecobaby mattress has a natural rubber core with organic cotton and Pure Grow wool quilted to organic cotton mattress ticking to keep padding from shifting (wool is used as a natural flame retardance, wool is naturally water- resistance, wool has natural bacterial resistance and dust mite control properties)quilted together and wrapped around the core. Natural rubber is firmer than other natural type mattresses. This makes our mattresses durable and comfortable. All of our crib mattresses pass all safety regulations and CPSC guidelines. NOTE: A crib mattress generally is composed of a foam core with vinyl covering. Studies have shown that mice on this mattress have a reduction of 26% of their airflow. A toxic, chemical laden mattress can cause irritation to nose, throat, eyes and can cause asthma like reactions or difficulty with beathing--This could be a major factor in SIDS. Many studies have confirmed the link between SIDS and chemicals but the crib industry is very large and keeps promoting cheap synthetic mattresses. (would you like to sleep on a vinyl mattress)$35 additional shipping is included in the price CRIBRUB standard crib(28x52")(we recommend the organic wool moisture pad and the organic cotton mattress pad to protect your babies mattress from wetness.