Using a carrier polymer that can be easily printed, like PLA, means that some of the properties of the additives which could not normally be easily 3D printed can be enjoyed.
The ratio of carrier polymer to additive will vary between manufacturers. An important consideration when selecting a composite 3D printing filament is that the higher the percentage of additive, the more abrasive the filament will be. This can lead to damaging the nozzle of your 3D printer. For high ratio composites this can only be avoided using a hardened nozzle.
You should also consider how much post-processing you want to carry out on your composite 3D print. To get the desired finish, some composite filaments will require extensive processing with rock tumblers and polishing creams whereas other composite filaments will require little or no processing to achieve the desired finish.
Copper composite filaments use copper particles to achieve a final product that looks realistically metallic. Copper filaments will nearly always require post processing, usually in the form of simple polishing with steel wool. If the composite is PLA based it will have a printing temperature anywhere between 190°C and 220°C. An added benefit of printing with copper composite filaments is that the copper particles dispersed in the carrier polymer increase thermal conductivity, allowing for quicker heating and cooling.