It's common knowledge that keeping a case on your laptop is great for protection but a hazard when it comes to overheating.
While cases protect your laptop from dents and scratches, it also helps it from getting too hot while in use. According to writer Jacob Clifton, "The case around your computer's guts is there to protect it from dirt and fuzz, which is one of the most common causes of overheating. Dust, pet hair, and all the rest of the daily grime are the biggest cause of PC temperature issues, because they interfere with the fans meant to cool your equipment down. If you've ever cracked a case open and looked at the fans inside, you won't have forgotten that grungy sight. Case closed, please."
Well ladies and gentlemen, there you go.