Doors and Windows - hollow vs solid - one last question

I appreciate the responses about hollow vs solid core doors in a previous post. My wife and I have decided to go with a mix of the two so all the main doors are solid core yet we stay within budget by allowing the closet doors to be hollow.

I need a final opinion on one other issue (quickly if possible - we're ordering tomorrow): I have two A/C units servicing the upstairs, and they are accessed through the upstairs main hallway. These are two doors I told him could be hollow since they won't be used by general traffic. I'm wondering now since they open to attic space if it would be smarter to go solid core for thermal insulating reasons.

Does the solid core add significant insulating characteristics over hollow core?

Thanks for all the help. I ask better questions of my builder thanks to this forum.

Yes they help in both sound and insulation.