Wires : Aluminum Foil Shield WireWires carrying electrical signals are often shielded to prevent radiation and signal loss and to reduce EMI/RFI interference. Aluminum foil shields use a thin layer of aluminum foil that is bonded to a polyester film. Aluminum foil shields are very good at reducing radio frequency interference (RFI), but not as effective on electro-magnetic interference (EMI). Aluminum foil shields are very low cost,making them an attractive option, however they are also very fragile. Aluminum foil shielded wire is often seen in coaxial cables used to carry telecommunications signals.