Should you use 15lb felt underlayment over OSB subfloor or can you use an insulate/sound proof .11" thickness underlyament instead of felt?

Dear Stac, Thank you for contacting us. Laminated rosin paper or #15 builders felt (tar paper) acts as a moisture retarder and may be used to reduce movement caused by changes in subfloor moisture, thereby reducing cupping and warping. (This is especially helpful over crawl spaces and basements.) In addition, the use of these materials can give the flooring a more solid feeling, reduce sound transfer, prevent noise caused by minor irregularities and debris, and make it easier to slide the wood together across the surface of the subfloor. Kraft paper may be used to make the installation easier but DOES NOT serve any other purpose. We do not recommend any other underlayment. For your convenience, below is a hyperlink where you will be able to review our recommended installation instructions. We hope this information is helpful. http://www.floorexpert.com/articles/Installation/Installation-Instructions-3-4-Solid-Hardwood-Plank-Strip-Products-for-mechanically-fastened-staple-nail-or-cleat-applications?retURL=%2Fapex%2FknowledgeSearch%3Fk%3D3%252F4&popup=false&lang=en_US&KBArticleTypeLabel=Installation&KBArticleTitle=Installation+Instructions+3%2F4%22+Solid+Hardwood+Plank+%26+Strip+Products+for+mechanically+fastened%2C+staple%2C+nail+or+cleat+applications&KBArticleName=Installation-Instructions-3-4-Solid-Hardwood-Plank-Strip-Products-for-mechanically-fastened-staple-nail-or-cleat-applications&KBArticleType=Installation__kav&KBArticleID=kA361000000MVuL