The need for rubber to aid the war effort was given in detail by the next two pages of the wallet.
It was called "The Rubber Situation". Facts are given for at least the year 1943 to include the year 1944. The "War Needs" as compared to the "Crude Supply" are listed, along with the hope that "synthetic" products will help meet the projected needs. All this was to allow the holder of the War Ration Wallet to a single pair of "Rubber Footwear".
My Dad tells the story that his Mom (my Maw maw) sent him the slip for shoes while he was stationed in Germany. His new shoes arrived, and in a short period (only worn once) they were stolen from under his bunk. Guess at this time, there were a lot of folks without shoes!