The most dangerous materials are ones that are porous and potentially toxic. These include jelly, rubber, PVC, latex, and most realistic or skin-like materials. I highly discourage you from using toys made of any of these materials, especially internally. If you want to throw a condom on them, again, make sure it’s polyurethane, but condoms aren’t made to protect against toxic chemicals and there haven’t been any studies to show that they do. You could totally use a condom and still experience the itching, burning, nausea, headaches, infections, and other issues these materials are known to cause.