Pool cue ferrules are the material that fits below the tip on a pool cue shaft. The basic function of the ferrule is to act as a buffer between the tip and the cue shaft to absorb the shock of the hit and to prevent the shaft from splitting.
The Juma and XTC ferrules, used by Schmelke Cues, are made from very strong thermocast materials. They are not only durable but have a very fine porous structure that resists absorbtion of chalk. Another characteristic is that they machine, glue and polish very well.
The downside to linen based ferrules is with their woven grain structure they more easily attract chalk.
Lastly many custom cues in the past have featured natural materials such as ivory and deer horn. Ivory, historically, has been one of the most popular materials for cue ferrules for decades. This is due to the natural and unique hit it provides. Ivory has a unique grain structure. However, due to the new laws regarding importing of ivory this material is no longer available.