I believe the "Matrix" you are referring to is as follows:
Self-regulating Heating Cable Polymeric Compositions A first conductive constituent is cryogenically cooled to a temperature at least as low as its glass transition temperature, and ground into first conductive pellets. A second conductive constituent is cryogenically cooled to a temperature at least as low as its glass transition temperature and ground into second conductive pellets. The first and second conductive pellets are then combined to obtain a mixture which is extruded over a pair of conductive wires to form a cable.
Please confirm that this is what you are looking for. Here is how these self regulating, matrix insulated heating cables are designed and work:
Design 1. A twin conductor cable incorporating an extruded self regulating semi-conductive matrix core is double jacketed with thermoplastic often with a tinned copper braid in between. 2. The heat output and regulation is produced by the combination of the twin parallel copper conductors which provide an electrical potential difference across the inner semi-conducting matrix core.
How They Work 1. The semi-conducting matrix core provides the self regulating heat output. 2. The matrix core adjusts its electrical resistivity and thus the heat output. When the matrix core is cold it conducts more electricity and thus produces its maximum heat output. As the matrix core temperature increases it expands and progressively increases it's electrical resistance thereby reducing its heat output. 3. This phenomenon allows the cable to adjust to the surrounding ambient conditions. e.g. If heat from the sun shines upon the floor heated with matrix heating cable, that particular area of the floor reduces its heat output. Likewise if a door is opened and cools the floor in one spot, the heating cable in that locally cooled area produces more heat.
Note - You may have to deal with Tyco Thermal Controls in your country in this regard. www.tycothermal.com/