Can you separate a 'flattened balloon' in a vacuum? If a flat, fully sealed balloon is in space, could you pull the walls apart quite easily apart from the elastic force? In other words, will a balloon go from flat to "filled with a vacuum" if it's in a vacuum? I'm thinking because there's a vacuum outside the balloon, there's nothing to "push" the walls of the balloon together and they should separate easily (aside from the elastic) but my gut says that's not possible. This is of course purely hypothetical and assumes a perfect vacuum and perfectly flat balloon etc
This is a very similar question below and has a nice answer which is kinda saying "nothing is not nothing because of quantum physics" but I feel the question was really just about the "inside" of a cube where my question is more about the inside and outside: given they're both equal/no pressure, then can the walls of the balloon move freely?
Is it possible to create nothing? 
 A: Balloons expand or contract due to pressure differentials.  When you blow up a balloon, the air inside pushes on the rubber harder than the air outside, so it expands.  When you let air out of a balloon, the air outside is pushing harder than the air inside, so it contracts.
In a vacuum, you should be able to easily expand or contract the balloon by physically pulling it open or squeezing it together, because there's no atmosphere either inside or out.  You may get an extremely minor pressure difference after repeatedly expanding and contracting the balloon, because even deep space isn't a perfect vacuum, but it should be negligible.
That answer you refer to is correct, even a true vacuum isn't totally empty thanks to virtual particles.  But these should be evenly distributed outside and inside the balloon.  If the balloon is made of a conductive material, you may have to fight the Casimir effect to expand it for the first few microns.  The Casimir effect is extremely weak, so it would be detectable, but not much of a hindrance.
