Soft rubber vibrators, which most people choose for penetration can be made of a variety of materials: silicone , jelly rubber , cyberskin, vinyl, and all manner of silicone/jelly mixes. One of the benefits of any soft rubber vibrator is that it will be quieter than hard plastic, and if you drop it, it’s less likely to crack.
Silicone is the best quality material for a soft rubber vibrator; it is the cleanest and safest material, it transmits vibrations best (so the motor will feel stronger), it is easiest to clean, and it retains temperature better than other rubbers. The only drawback to silicone is the cost. Also you cannot use silicone based lubricants with a silicone vibrator.
Currently most jelly rubber vibrators contain phthalates and should always be used with condoms. These along with latex vibrators, which are usually filled with foam, absorb vibrations a bit more, so they tend to be milder than silicone or hard plastic. The main benefit of these vibrators is their inexpensive price.
There are some vibrators that have a hard plastic shell which is then covered in a softer material like silicone or jelly rubber. These vibrators often have the benefit of strength with the softer feel which some people prefer.
Learn more about sex toy materials.
