A coaxial cable consists of four basic components: a center conductor, down which the signal travels; a dielectric; a shield(usually aluminum); and an outer jacket. Shields intercept electromagnetic energy that enters the cable and shunt it to ground, which prevents it from reaching the center conductor where the signal is sent.
There are several types of shields, each with their own characteristics. Foil is the most common, but it's not always the best choice; braided wires have many advantages over foil in areas such as conductivity and connectorization. Generally speaking, the more shielding a cable has, the less loss it experiences. More shielding also means it can withstand hacks and other damage better than less-shielded cable.
The most popular type of shield is foil, and it's commonly found in RG6 cables. Braided shields are much more variable, however; they may be a single aluminum braid with just enough braid to help connect the connector, or they could be a multi-layer braid with 40% and 60% coverage braids, for example.
Both types of shields have their pros and cons, but the best choice for most applications is a dual-shield cable. There are situations where more shielding is required, such as when installing a coax in a location with high electromagnetic interference or radio frequency interference (EMI/RFI). But for most applications, a dual-shield cable will deliver the performance you need at a price you can afford. So choose a cable that is right for your application and get it installed correctly to maximize performance.
