Hi there and thank you for your question.
Greg above selected product Pergo XP Alexandria Walnut 10mm Thick already has an underlayment attached to it.Should you use felt or not really depends on your geographical location and structure of your home.We would need to know a little bit more about your home in order to give you a real and sensible answer in regards to vapor barrier (felt) installation. I would recommend visiting our How-To-Community (www.community.homedepot.com
) and posting this question. I'm positive that one of our in house experts will post back to you shortly.
Hope this helps.