There are current products on the market that use a silicone sheathed catenary heater. This system will work and heat the catenary line typically at a 10w/ft to 15w/ft range. The problem with silicone can be seen in the roofing heat trace market – a fungus can grow on the silicone.
This fungus by itself is not a problem but certain birds have an appetite for the fungus and can inadvertently destroy the heater. This is the reason the heat trace elements in the roofing market have eliminated silicone as a solution – no silicone – no birds!
The NIBE Element Railway Solutions Blue Wire catenary heating element sheathing is not silicone based - it is sheathed in a TPA compound with extremely high electrical isolation properties. It is then surrounded by a steel braiding followed by insulation and then the braided heating alloy wires.