Wood flooring underlay paper

Q: I am installing a hardwood floor in both of my bedrooms. I have a subfloor down. Is there anything else that I might need to put down prior to laying the hardwood? I purchased some felting to reduce the sound. Then I was told that I didn’t need the felting.

I am so confused.

A: Use wood flooring underlay paper. The boards will move into place much easier with it down. It also serves as a moisture retarder.