Section 2: Equipment

All balls used in a match must have the same characteristics regarding circumference, weight, pressure, type, and color (Rule 3.3). In FIVB World and Official Competitions, three balls are used.

Source: Rule 3, Rule 3.1, Rule 3.3, Rule 3.4, Rule 2, Rule 2.1, Rule 2.2, Rule 2.3, Rule 2.4, Rule 2.5, Rule 4.3, Rule 4.3.4, Rule 4.3.3, Rule 4.3.5

Send this to your friend — argument over.