Ferrules

Pool cue ferrules are the most commonly white material the fits below the tip on your pool cue shaft. The basic function of the ferrule is to act as a buffer between the ferrule and your cue shaft to absorb the shock of the hit.
Along with the tip and shaft type and taper the ferrule has a lot to do with how your cue hits and performs.
The most popular type of ferrules are linen based basted ferrules or linen melamine variants such as Aegis, Ivorine or Standard linen melamine. These type of ferrules have a very strong and durable and machine and glue very well. The downside to linen based ferrules is with their woven grain structure they more easily attract chalk.
Also popular are various thermoplastic variants such as XTC, and titan. These types of ferrules provide a softer hit and are much lighter providing more low deflection properties. These types of ferrules are cast and not woven so they are easier to keep clean and less chalk absorbent. They are not as durable as linen based ferrules.
Lastly many custom cues will feature natural materials such as ivory, and deer horn. Ivory has been one of the most poplular materials for cue ferrules for decades do to the natural and unique hit it provides. Ivory has a unique grain structure and most often is installed with a cap and spacer to provide added strength.