Underfloor heating wires are made up of a number of separate elements to enable them to heat safely and comply with the electrical regulations. The most important element of the cable is the resistance wire or wires which provide the heat when the system is turned on. The heating wires will also have a layer of electrical insulation around them for safety.
The heating cable will also contain an earth that ensures if there is any damage to the cable the RCD will sense this and ensure the system is turned off.
Most cables will also include a strong thread to ensure the wire cannot easily be stretched and damaged.
Finally, a layer of outer insulation is used which has two purposes. The outer insulation is used to ensure the heating cable meets the electrical safety requirements and additionally this insulation layer guards against damage during installation which otherwise could be caused when people install or walk on top of the wire.