Core : rubber, around 4mm thick.
Pressure : pressurised to around 0.8 bar.
Seal : silicon.
Felt : made of wool, cotton and synthetic fibres. The felt cover represents 20% of the weight of the ball (it is around 3mm thick).
Two types of felt can be used to cover tennis balls and they heavily influence the aerodynamic behaviour of the ball:
- "Needle" = mainly non-woven synthetic (acrylic) felt.
- "Woven" = "warp and weft weave " rich in cotton, wool and polyamide.