underlayment for floating floors is a very important piece of the flooring puzzle
Well with the title to this entry it should be clear that I believe the underlayment for your floating floor is CRITICAL for your floating floor.
Depending on the application of your flooring there are a number of options.
The best advice I can give quickly is that you should match your flooring underlayment with the “mission” of the floors.
For example if you are just finishing an extra room in the basement that is used infrequently you can just use the basics. But know that it will echo more so than a glue down floor or a floating floor that has a more sound dampening characteristics like a 6mm cork underlayment. (NOTE: FOR ANY CONCRETE APPLICATION IT IS REQUIRED TO USE ADEQUATE MOISTURE BARRIER. THIS IS NOT AN OPTION!) Some foam now has moisture barrier built in which works, but make sure you follow the rules.
If you are doing an upstairs room that you are worried about sound you should really concentrate on what is the best sound dampening material for you. I think that the Sound 6 barrier as well as the 6mm cork represent the best of the best.
Always feel free to run your project by an iFLOOR expert so that you understand what is best for you.
http://www.ifloor.com/group_11559/more-/flooring-underlayments/underlayment.html