[Greenbuilding] flooring underlayment

[Leanne Rellstab]

Hi,

I was curious to know what product is preferred for flooring underlayment.  The building is designed for 3" concrete floors.  But some of the floors will be wood, cork, or marmoleum.  I was going to put in sleepers (2x4's) to build the floor up even with the concrete, then an underlayment, then the finished product.   What should I use for the underlayment?

LMcClain