Cementing plugs | Wiper Top & Bottom
Cementing plugs are semirigid barriers used to separate cement slurry from drilling fluids, to wipe the casing, and to indicate when cement placement is complete. Plugs were once made of gunnysacks, wood, and leather. Present designs include top and bottom wiper cementing plugs constructed of nitrile or polyurethane molded over PDC drillable high-density plastic cores (Fig. 1). Most plugs are designed to be nonrotating; as a result, they are easier to drill out (Fig. 2).

Fig. 1.
https://www.drillingmanual.com/cementing-wiper-top-bottom-plugs/