from G-Stahl.com:

Just as many other MacBooks, mine got really hot and that got me a bit concerned. This is my first Apple laptop and I take a lot of pleasure in discovering new things about it. After playing around with it I found that the vent under the screen is covered with a piece of laminate. I briefly checked the manual and it doesn’t mention anything about it. It’s very hard to get to it as the gap between the screen and the base is very tight. However, I was able to remove it and surprise… my fans went quiet. The laminate covers the whole vent so no air gets out at all.