Good conductivity is important to allow electrical current to flow more easily without resistance through it. Copper is the material used as the conductor material in interconnects due the fact that it has a high conductivity, compared to the other common materials that are used. The purer the copper the better conductivity you will have. The only time that this would not hold true, is if the only impurity in the copper is silver (silver is actually more conductive than copper). Some wire manufacturers combine silver with copper to make up the conductor material.

All material no matter how conductive does offer some resistance to the flow of electrical current, so the electrical current traveling through the conductor is just like you climbing a hill. The longer and steeper the hill, the less energy you have when you get to the top. So keep your interconnecting cable as short as possible, as there are other things working to keep the signal from getting from A to B.

To provide a high definition picture, a lot of data must be moved along the HDMI cable; the higher the resolution the greater the data. To move a vast amount of data across a cable in a small amount of time, you have to move it fast; the more data the faster you have to move it, which causes a phenomenon know as the “skin effect”. As the speed of current flow increases, the current flows move from the core of the conductor to the outer surface of the conductor. Some current on the outer surface of the conductor does not reach its destination as it is absorbed by the insulation material. Unfortunately, no insulating material provides 100% resistance to the flow current, so some of the signal wanders into the insulation and get lost. Technically speaking, the best kind of insulation is a vacuum, and then air would be next in line. Using a vacuum or air as an insulator is not practical for home use, even in 2008, and the next best insulator semi-solid dielectric is not currently being used. Next in line is foamed dielectric. You will find foamed dielectric used in some HDMI cables. What are typically used as insulation in most HDMI cables are solid dielectrics. Generally, solid dielectrics that surround conductors are plastic composites, with polystyrene (better) and polyethylene (best) being the superior materials. Teflon is actually considered the best solid dielectric, but I don’t think you will find it being used in HDMI cables; unless it is being installed in aircrafts.

Trying to keep the signal you want in is not the only insulation challenge; you also want to keep unwanted signals out. EMI (Electro-magnetic interference) is also a problem, and it is attracted to the conductor material. EMI causes unwanted noise to arrive at the receiving end of the wire along with the desired signal, and if the noise level gets too high it may drown out the signal. If you have even been in a night club, and tried to have a conversation standing next to the loud speaker, you understand what I am talking about. You probably had to repeat parts of your conversations several times, to be heard and understood. Even though it is aggravating, your message is eventually received and understood by the recipient, or you just move away from the speaker and continue your conversation. Your interconnecting wire can’t do that; it can’t just pickup and move to a quieter environment. With digital data in an IP network, having to repeatedly re-send data is not that big of a deal (the IP protocol actually allows for that); things just run slower, or things arrive out of order and are re-assembled before it is rendered. With real time sound and video that is a problem. You can’t really wait for re-sent information to arrive. The sending device just keeps sending data at its output rate, and the wire and the receiving device just has to keep up. So when the signal the receiving device needs does arrive in good enough quality, you get no or garbled sound, see frozen images, a blank screen, or a bunch of little squares.

Look for Teflon, Mylar foil and copper braiding to surround individual data channels to stop individual channels from interfering with each other, and to keep external EMI from entering the signal path. Better cables will use those materials and other techniques in combination to block as many different frequencies of EMI as possible.

The ends of your interconnecting cables make the connection to your devices. To allow you to easily connect and disconnect cables, the connection between cable end and device is of the surface to surface type. Gold has the best surface to surface conductivity, so you will typically find gold connector points on your better AV components and your better HDMI cables. The connection between the connector ends and the conductor is also of critical importance. Unfortunately you will have no way of inspecting this aspect of the cable you choose. The internet can help you with this; try a few searches on your chosen cable to see if there are frequent report s of cables that mysteriously stop working without any change in equipment or setup. This is an indication that the conductor and connector ends have a tendency to separate.

Another issue to be aware of with HDMI, if you are using heavily shielded cables that are heavy and bulky, be sure to use some kind of strain relief near the cable and device connection. Due to the current design of the HDMI cable to device connection, heavy cables have been known to cause the cable / device connection to become loose or separate completely.