Silicone is non-porous and can be sterilized. It's also free of harmful chemicals like phthalates, and potential allergens like Latex. The same can definitely not be said for rubber -- rubber can hang onto bacteria, causing infections, and cannot be sterilized. Some rubber varieties, like jelly, contain chemicals that can cause burning, itching, or worse. Many materials, like jelly rubber and PVC, are harmful to the environment during their manufacturing process as well as during their long slow death in a future landfill -- and since they only last a few months before they need to be thrown out, there are plenty in landfills.