One of our super-friendly sales reps, Matt, wrote this up in response to interest from our customers:

We often receive questions about the difference between QuietGlue Pro and Green Glue sound isolation compounds. Due to a real difference in cost, many customers wonder if the more expensive Green Glue really outperforms the competition. Both Green Glue and QuietGlue Pro have conducted third-party tests comparing the two products head to head, and both companies claim that their product is superior based on those test results.

After reviewing the results, we conclude that their performance is too close to crown a true winner. When it comes to sound isolation, the STC rating is what’s really important, and the STC of QuietGlue Pro and Green Glue are almost identical. So close in fact that choosing one over the other based on performance doesn’t make sense.

Since they are tied on performance, it makes sense to choose on price, and at least for now QuietGlue Pro wins the price battle hands down.