For thermocouple extension and compensation cable we distinguish 2 types of conductors: stranded and solid conductors.
What are solid conductors?
Solid conductors are made of one single piece of wire, such as the thermocouple wire. The solid conductors are rigid and simple. Due to the thickness of the wires, they have a high resistance. However, they are also quite prone to breakage since they are not as flexible as standed wires. Solid conductors should therefore be not used at sites with many bends. Mostly, solid conductors are used for heavy duty applications.
What are stranded conductors?
Stranded conductors are made of several small gauge thermocouple conductors bundled together. This makes them very flexible in comparison to solid conductors. Stranded conductors can withstand vibrations and flexing quite well without risking to break. However, the stranded wires are susceptible to corrosion, and they tend to be more expensive due to complex manufacturing process. In addition, stranded wires require some technical knowledge before they can be successfully soldered.