To the general person, indoor and outdoor pickleballs might look very similar.
Once you've held an indoor and outdoor pickleball or had them side by side, the differences become glaringly apparent. In general, the majority of indoor and outdoor balls are unique in the following ways:
Number of Holes: Indoor balls have 26 holes while outdoor balls have 40.
Hole Diameter: Indoor balls have holes with wider diameters than outdoor balls.
Weight: Outdoor balls tend to be heavier than indoor balls.
Hardness: Outdoor balls tend to be harder plastic than indoor balls, aiding with more bounce.
Durability: Because outdoor pickleballs are harder they tend to crack quicker than softer indoor pickleballs.