Most practice golf balls today are different from the whiffle balls that were used in the past. Today's practice golf balls are designed to act much like a normal golf ball, except that they are designed to fly no more than 40 feet. This gives them the feel of a normal golf ball, and it allows you to have a more effective practice time when away from the golf course.
Many practice golf balls are made out of a dense foam rubber, such as the Point 3 Almost Golf practice balls. This limits the amount of energy transferred to the ball, which helps restrict the flight of the ball. It also makes the ball lighter than a normal golf ball, which is one of the drawbacks. Some practice golf balls aren't even shaped like a golf ball, such as the BirdieBall, meant to improve swing mechanics.