Avengers Space Suits

The space suits worn by the Avengers were designed by Tony Stark, and are individually customized for each hero to allow them as wide a range of the exercise of their abilities as possible. 

 For example, the Wasp's suit is designed to be able to channel and amplify her bio-energy blasts and allow her Earth-bound reflexes for flying to be translated to space propulsion, even though there is no air for her wings and their beating action would otherwise set her to spinning.

The Hulk's space suit consists primarily of a breathing apparatus, as his skin is dense enough and his regenerative abilities fast enough to allow him to operate in space without dermal protection.  The materials of any suit would likely not stand up to his particularly brutal style of combat in any case.