Selecting strings can be a confusing and expensive task. A basic understanding of strings and how they are made will help in making an informed choice. The string core is what primarily affects the sound of a string. Strings are typically made with one of the following core types; solid steel core, stranded steel core, synthetic core, gut core.
Solid steel core is relatively bright, has a clear sound and an easy bow response. Steel core strings have a quick break-in time and are stable and durable.
Stranded steel core has a warm clear sound, quick and easy bow response and also has a fast break-in time and is very stable and durable.
Synthetic core strings have a warmer richer sound than steel and is more durable than gut core strings.
Gut core has the warmest sound and richest tone, but is slow to break in, less stable and the least durable of all the string core types. Gut core is recommended for advanced players only.
After the core material is selected then the wrap wire is selected. The wrap wire is used to add mass to the string to achieve the proper pitch and tension. Different metals are used for each string depending on the durability of the material and the weight. For example, a cello C string often will use tungsten because tungsten adds a lot of weight in a very small area. The smaller the string diameter, the faster the bow response.
Next, strings can come in various tensions, light, medium, heavy or some other adjective to describe tension. The lighter the string tension, the more dynamic range. The musician can play closer to the bridge and closer to the fingerboard to cover a larger dynamic range while playing. A heavy tension string will give a larger overall volume, however, it will be more limiting in dynamic range, it will be more difficult playing closer to the bridge or fingerboard. Medium tension is in between light and heavy and is always a good place to start. So first, decide what kind of sound you are looking for, then what kind of bow response you need and read the string packaging to find out what the string is made with to determine what kind of string will best suit your needs.