The Hollywood actor - who is married to actress Scarlett Johansson - thoroughly enjoyed filming the scenes with his 'The Proposal' co-star because she has a great body.
He said: "It's a good situation to be in, seeing her naked - believe me, Sandra's no slob, that's for sure!"
The 32-year-old hunk initially worried Sandra, 44, would back out of the scene because of nerves.
He explained: "I didn't think we'd shoot it to be honest, because she's never done a head-to-toe nude scene before. I just thought, 'Oh she's just going along with it and once we actually get closer to it, she'll say we need to rewrite this.' No way. She was 100 per cent in. About two weeks before we were having dinner after work and I said, 'Seriously, are we doing the nude scene or what? Are you really going to do this?' And she said, 'Absolutely!' "
The pair - whose on-screen personas accidentally bump into each other while naked in the film - found the scene so entertaining, they gave it a nickname.
He added to Britain's More magazine: "It's nudity and stunts combined - we call them 'nunts'! It actually helps when you're friends, because after a few hours, you're laughing about it. You're having these mundane conversations and the only difference is you're not wearing pants. She just had on the little postage stamp things and I wore a flesh-coloured pouch. It was really, really awful!"
Related Gallery: Ryan Reynolds and Sandra Bullock in 'The Proposal'
