Don't eliminate the possibility that a lot of stuff marketed as silicone may contain other polymers that are not as heat-resistant.
A large fraction of cheap "silicone leads" are actually just overly plasticized polyvinyls.
Not only do they burn at temperatures many real silicones can handle, the plasticizer tends to leach out, and if you store the leads in a plastic container (or even a plastic fabric pouch), they can fuse into the container. (The plasticizer then acts kind of like a solvent, melding the two plastics together at the molecular level.)
In the kitchen, ovens can traditionally reach 260°C = 500°F, which is just slightly higher than "standard" silicones, into the "high-temperature" silicone range. As there is no price difference between the two, really, there are kitchen utensils made of silicone that can handle such temperatures. It's just difficult to discover which ones do, without testing them.