Celtic have yet to concede in the league this season and Forster believes it is the basis for a successful team.
"It's fantastic to keep clean sheets whatever you do," he added. "There has been a massive change in players this summer so it will take a bit of time for everyone to get to know each other. But everyone did brilliantly against Hearts.
"You defend as a team but if the back five is strong it allows lads to bomb on and create chances. We could easily have scored more."