This amazing video demonstrates what would happen to a marshmallow man in space. Since space is a vacuum the air inside the marshmallows expands due to the absence of air. Watch how big this guy gets.

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There have been at least two accidents of Humans beein exposed to high vacuum levels in vacuum chambers.
One i know of the special suit the guy was wearing failed, so he was exposed to the vacuum. Another person in the room grabbed the Weapon of a security guard and shot a glass of that chamber so air could get back in.
He survived, but that day still sucked for him i guess.
So the Human won't explode, that only happens in Hollywood.
A Human can survive a vacuum for a short amount of time.
AFAIK it is necesarry not to try to hold the breath, because that could infact rupture the lungs.
But i still don't recommend trying a vacuum on yourself anytime soon tho.
http://www.instructables.com/id/The-InstructableSlideshowVideo-Tabs..../