Ok thanks. I will definitely call them. Currently, I believe (and will confirm this weekend when I tear out the carpet in the first room) that they have Luan down underneath the carpet. I'm hoping since the floor is only 13 years old, that this is still in good shape and is re-usable. Because of my squeaking issues, I had someone recommend putting another 3/8 sheet of sanded plywood down as hoping to quiet the squeaks in addition to adding screws, etc. But the underlayment I'm talking about is just the one that Pergo makes. The outlast comes with the backing already and this type of underlayment is the only one Pergo will allow to put under and keep the warranty. The main reason for the underlayment is a bit of a sound barrier for underneath (my next project is finishing the basement and I want to do all I can to minimize noise underneath) and for minimizing sound walking on it as far as hollowness or something like that.