How to judge laminate flooring underlayment

[Bob H.]

I'd like some expert opinions about cost vs. quality of various kinds of underlayment for laminate flooring. I am about to install flooring in my own home.

Choosing underlayment seems similar to what I read this morning about the market for cybersecurity software. The expert being interviewed characterized it as a situation in which buyers don't understand what they're getting and can't tell whether a product is effective. 

With underlayment, people state what seems obvious -- that a thicker product will do a better job of deadening noise and perhaps of blocking moisture penetration through a concrete slab. Others speculate about the possible destabilization of the flooring with a thick underlayment: Would it let the flooring flex and work apart at the joints?

That's about as far as it goes. A demonstration panel I saw at a store, allowing customers to tap on four samples with a small mallet, was marginally informative. At Home Depot alone, I saw some underlayment that sells for 25 cents a square foot, another kind for 50 cents and a third product for 65 cents. These are big differences. The question really is: Is the 50-cent product really twice as good (whatever that means) as the 25-cent product? Is the 65-cent product noticeably better than the 50-cent product?

If you have installed the same flooring in similar locations, with the only difference being the underlayment, I'd be very interested in knowing whether anyone, without prompting, would notice the difference and, if so, whether the expensive underlayment really was better.