I don’t think there is any suitable replacements for No Res. It’s the only product like it on the market. Alternative like ones offered at Part express is a multi-layer.. with a layer being in the middle witch of I’m hearing correctly can possibly add reflection problems.
Essentially I think this No res is all one material, as it looks like a portion of the foam is heat compressed maybe, like a good half inch maybe or more. Which makes the backing, then the layer of pressure sensitive adhesive is added to the back. Making it all one material and such. Just my guess making it easy to use with many applications.
Not really a close substitute, but something that can work not as good but will get you by. Go to Home Depot or Lowe’s, and grab a sample or two of the flooring.. the faux wood floors with stick backing. If your carful you can split this sticky layer off. Then, attach a flooring foam to the other side or a dense open cell foam. The carpet padding is better. If your in a pinch, have a long area to do, this method I’ve seen used and people happy.
For the extra efforts, cost of gas, then spray glue, an foam… time and cost, your better off with No res.
Can’t beat it for the price.