What are NFL footballs made out of?

Despite being in use from the dawn of the sport, the phrase "tossing the pigskin" is not as accurate as it used to be. NFL footballs used to be made out of pig hide, which is where that phrase originated. But as the sport grew more and more popular, scientists eventually researched and developed a perfectly weighted and proportioned ball for the sport.

So exactly what are NFL footballs made out of? The truth is that these footballs are now made out of leather. It seems like the saying should be changed to "tossing the cowskin" but to no avail, tradition in American culture is quite difficult to change.