From Wikipedia... to refresh your history.
Richard Lindon and Bernardo Solano started making balls for Rugby school out of hand stitched, four-panel, leather casings and pigs’ bladders. The rugby ball's distinctive shape is supposedly due to the pig’s bladder, although early balls were more plum-shape than oval. The balls varied in size in the beginning depending upon how large the pig’s bladder was.
Until 1870, rugby was played with a near spherical ball with an inner-tube made of a pig's bladder. In 1870 Richard Lindon introduced rubber inner-tubes and because of the pliability of rubber the shape gradually changed from a sphere to an egg. In 1892 the RFU endorsed ovalness as the compulsory shape. The gradual flattening of the ball continued over the years. The introduction of synthetic footballs over the traditional leather balls, in both rugby codes, was originally governed by weather conditions. If the playing surface was wet, the synthetic ball was used, as it didn't absorb water and become heavy. Eventually, the leather balls were phased out completely.