A rubber plug used to separate the cement slurry from other fluids, reducing contamination and maintaining predictable slurry performance. Two types of cementing plug are typically used on a cementing operation. The bottom plug is launched ahead of the cement slurry to minimise contamination by fluids inside the casing prior to cementing. A diaphragm in the plug body ruptures to allow the cement slurry to pass through after the plug reaches the landing collar. The top plug has a solid body that provides positive indication of contact with the landing collar and bottom plug through an increase in pump pressure.