Jelly is a blend of polyvinyl chloride (PVC) and rubber used to make sex toys, including vibrators and dildos. It's a popular sex toy material because it's inexpensive and able to be formed into virtually any shape. It gets its name for its soft texture and feel, which resembles jelly.
This finish comes from the addition of softening chemicals known as phthalates. The more rigid the jelly sex toy, the fewer phthalates it's likely to contain. Phthalates have potential health risks and can cause allergic reactions in some people. However, these risks can be reduced if you use a condom with your jelly toy.
Jelly is a porous material so jelly sex toys can harbor bacteria. They should be cleaned thoroughly after every use to avoid infections.