The compound is a reference to the rubber that the tyre’s wearing surface is constructed from.
Pirelli is the exclusive supplier of tyres to Formula 1 having secured the contract in 2011. The range consists of... has developed a suite of compounds from C1 refers to the compound of the rubber that the tyre's wearing surface is constructed from. Pirelli has developed a... (hardest) to C5 (softest) and they select three of these compounds for each race weekend. The selection is based on factors such as track surface, track temperature, speeds, corners and number of pitstops targeted.
Typically three consecutive compounds are used but this is not always the case. In Melbourne 2022 Pirelli supplied a step in the range as noted in formula1.com
This weekend will see the teams use an unusual mix of compounds: the C5 (Soft Tyres, or Softs, are identified by their red sidewalls and are one of three compounds available for each race.... x8 sets) for the first time this season, then a step to the C3 (medium tyre, x3 sets) and the C2 (hard tyre, x2 sets