While there is some rubber inside a pneumatic golf ball, its not a solid "rubber core" ball because its center is a rubber bladder full of air!  But what also sets this ball apart beyond its core is its cover is one of the few made from para rubber, not gutta percha.

“The Pneumatic” is marked on one pole and the 1902 patent date on the other. 

The Goodyear Pneumatic ball was covered under a patent filed on August 19. 1902 by Addison T. Saunders who assigned half of it to Frank Seiberling, the man who founded Goodyear Tire &Rubber in 1898.

The making of this ball was a bit of a marvel in and of itself.  According to the attached 1905 advertisement, the wall of wound thread between the cover and the pure Para Rubber “jacket” that held the compressed air consisted of a single thread of Sea Island cotton over one thousand feel long that was wound with perfect accuracy and uniformity.  The cover of the ball was also made from pure para rubber.

In the center of the ball, inside the para rubber “jacket” is compressed air. The accompanying ads show the core of compressed air and the other layers.  The first advertisement is a Goodyear ad from 1903.  The second was run in 1905 in the UK by the London firm of Geipel & Lange. Notice how Geipel uses Goodyear’s exact illustration of the ball.

Pneumatics are one of the most creative golf balls produced