Here is an interesting fact:
In an NFL game, if the game is indoors in a dome, the referee crews use twenty-four regular NFL balls and twelve k-balls for kicking and punting only. They enforced these special balls due to abuse of the regular balls like rubbing down the balls, even putting them in a microwave and too many touchbacks. The k-balls were enforced in 1999 to have more returns and fewer touchbacks and field goals that were high using the regular balls are down by in-between 40-45%. The kickers and punters are doing their best to get rid of the balls saying they are slippery, soft, there have been more fumbles since the k-balls were introduced, and teams lost games (whether crucial, regular, play-offs, and Super Bowl games) remember the Giants-49ers game where the 49ers led by a point and the long-snapper snapped the ball over the holder-punter's head and he had to throw it and got an interception back in the 2003 play-offs. The same balls with twelve are used for outdoor games but instead of twenty-four regular NFL balls, they use thirty-six balls instead. The k-balls are shipped in a box and aren't used until game time. Interesting fact!!