Best Underlayment for engineered wood floating floor
I am putting in a 1/2" engineered wood click-float floor over a wood subfloor, and need to select an underlayment for it. My primary concern is not pass-through sound to the floor below or thermal insulation quality, but rather having a floor that sounds like solid wood when walked on. I have read many posts on this and other forums of people speaking very highly of the FloorMuffler product for achieving a "solid wood floor sound," even though it is only 2mm thick. Is this product still better than a cork underlayment? 6mm cork is three times the cost of FloorMuffler, but I would spend it if it created a better result.
Also, does a 6mm cork underlayment sound any more "solid" than a 3mm cork? And what can you tell me about the IIC and STC ratings? I am of the belief that the IIC measures the product's ability to absorb reflective sound, thus making it sound more "solid." Does a higher IIC number indicate a better product? Any help that folks can offer would be greatly appreciated.