system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: how can you have double vacuum pressure to test a space suit?

Elon Musk just instagrammed the new SpaceX suit - it looks fresh!  He said "Already tested to double vacuum pressure" - my head is having trouble understanding how a "double vacuum" is possible.  Is it not just "no atoms are in that space" - how can you have "double no atoms in that space"?  Thanks!
gpt
All that really matters is pressure differential. 

If you have a pressure of 1 atm inside the suit, and vacuum outside the suit (0 atm, or close to it), you can make sure the suit will be able to hold up and not pop like a balloon.

However, if you didn't want to put it in a vacuum chamber, you could just pressurize the inside of the suit to 2 atm, so the internal pressure is 1 atm greater than the surrounding environment. The forces experienced by the suit are essentially the same.

So "double vacuum pressure" just means they tested a 2 atm pressure difference between the suit and the environment. That could be pressurizing the inside of the suit to 2 atm in a vacuum chamber, pressurizing it to 3 atm in normal air, or some other combination. This allows them to be extra sure that the suit won't rupture if it is exposed to vacuum.