As the NFL continues its investigation of the New England Patriots, following denials by both Patriots’ coach Bill Belicheck and quarterback Tom Brady that they knew the team was using deflated footballs in Sunday’s AFC championship game, former NFL quarterback Hugh Millen detailed how and why the air pressure inside footballs was important.

In a video posted by the Associated Press, Millen illustrated and described the differences between balls inflated to the NFL’s mandated inflation levels, between 12.5 and 13.5 pounds per square inch, and the reduced levels reported by referees in the Patriots game Sunday against the Indianapolis Colts. The main difference, according to Millen, is that deflation allows for better grip, especially in cold weather.

"If you're going to be challenged to handle the ball in either very cold conditions or wet conditions, then having the ability to grab the ball and squeeze it, you're going to have more of a chance to remain in contact with the ball," Millen said in the video.

Deflating a football can also increase the speed at which a quarterback can throw it, Millen said. Because of the softer grip, the index finger can stay on the football a bit longer, which allows for faster spirals during a throw. That’s particularly important for QBs who like to keep their fingers on the seam of the ball. "We know from having put a football in wind tunnels, the faster the ball rotates, the more it cuts through the air. It has less drag, therefore more velocity on the ball," Millen said. "Most quarterbacks like to have less air than more air."

Millen, who played briefly for the Patriots, was mainly a backup during his playing days in the NFL. He played from 1986 to 1995 with the then-Los Angeles Rams, Atlanta Falcons and Denver Broncos, according to

In separate press sessions Thursday both Brady and Belicheck denied purposely deflating the balls or having knowledge that the balls had been deflated.

"We will take steps in the future to make sure we don't put ourselves in that type of situation again," Belicheck said.

According to ESPN, the league found 11 of the 12 of the balls supplied by the Patriots to be under-inflated.

See Millen explain in the video below.