The first football was a pig's bladder, inflated with human lung power, and knotted at the end like a balloon. Boot and shoemakers then made a leather case for the ball, reflecting the shape of the bladder. This was "plum shaped"; rounder than today's rugby ball, but certainly not spherical.
In 1862 came the invention of an india rubber bladder and a pump with which to inflate it. This allowed the production of a round ball, though some manufacturers still had a button at each end of the ball to hold the stitching together at the point where the leather panels met. "Buttonless balls" was a prime marketing buzzword for suppliers and manufacturers in the 1880s!
There was nothing in the early rules about the size of the ball to be used. Some of those used in the "village" kickabouts were enormous by today's standards. To quote the Brighton College Football Song:
And Eton may play with a pill if they please
And Harrow may stick to their Cheshire Cheese
And Rugby their outgrown egg, but here
Is the perfect game of the perfect sphere
It was the practice on mainland Europe, at least until the 1940s, to use a smaller sized ball, the number 4. The England team were somewhat bemused to be asked to play with a no. 4 in an international in Portugal in 1947. They finally persuaded the referee to use a no. 5, but after Tommy Lawton had opened the scoring for England, the players found a no. 4 had been substituted! England won 10-0, so it didn't help the Portugese much!
The finalists in the first World Cup Final in 1930, Uruguay and Argentina, could not agree on the size of ball to be used. Different sized balls were used in each half!
Though the old leather balls could be treated with dubbin in order to keep them in good condition, they usually became waterlogged and heavy in wet weather. Modern balls have a waterproof coating.
Anyone able to visit the Gilbert rugby museum in Rugby, England will find a fascinating display of early balls, soccer as well as rugby. The museum is just opposite Rugby School. I believe a craftsman is often to be found in the museum, demonstrating the art of stitching a football.